the magnetostratigraphy of leg 73 sediments abstract the main objectiveof dsdp leg 73 was to obtain high quality records of major paleooceanographic events in the south atlantic this was achieved by coringsix sites on the african plate the sediments thus recovered span the cenozoic and five of the six sites proved ideally suited for magnetostratigraphic analysis the results presented in this paper and elsewhere in this volume constitute the first opportunity to extend the direct correlation of the magnetostratigraphic and biostratigraphic time scales into the paleogene in deep sea cores the magnetostratigraphic analyses from dsdp leg 73 sediments are presented in this paper the correlation of the magnetostratigraphy to the magnetic polarity time scale provides tight age depth control for the five sites analyzed allowing the accurate calculation of sediment accumulation rates the data presented here represent a remarkable record of the fine scale polarity history of the earth s magnetic field these data place constraints on the interpretation of small scale marine magnetic anomalies which are modelled equally effectively by field intensity fluctuations as polarity reversals at least some of the tiny wiggles correspond to very short polarity units in the magnetostratigraphic record by assuming an axial geocentric dipole the inclination of the time averaged magnetic field recorded in the sediments can be used to calculate the paleolatitude at which the sediments were deposited combining the age and average inclination information available from the magnetostratigraphy we present paleolatitudes versus time for the leg 73 drill sites

40ar 39ar dating and magnetostratigraphic correlation of the terrestrial cretaceous paleogene boundary and puercan mammal age hell creek tullock formations eastern montana the recovery and subsequent prolific radiation of mammals in the northern western interior of north america following the cretaceous paleogene k p boundary is well documented in rocks attributed to the puercan land mammal age the most complete puercan record is that of the tullock formation which crops out widely in garfield and mccone counties eastern montana the tullock formation overlies the dinosaur bearing hell creek formation and consists of a stratigraphic series of channel and overbank deposits from which well preserved puercan faunas have been collected these channel deposits are typically bracketed by widespread coal beds the irz and z coals mark the base of the puercan at the k p boundary as defined by the highest appearing local occurrences of in situ dinosaur fossils the highest stratigraphic occurrence of cretaceous pollen and an anomalously high concentration of the element iridium ir the irz coal is overlain sequentially by the z hfz y w and u coals fossil vertebrates

synchronizing terrestrial and marine records of environmental change across the eocene oligocene transition records of terrestrial environmental change indicate that continental cooling and or aridification may have predated the greenhouse icehouse climate shift at the eocene oligocene transition eot by ca 600 kyr in north america marine terrestrial environmental change asynchronicity is inferred from a direct comparison between the astronomically tuned marine eot record and published 40ar 39ar geochronology of volcanic tuffs from the white river group wrg sampled at flagstaff rim wyoming and toadstool geologic park nebraska which are type sections for the chadronian and orellan north american land mammal ages we present a new age model for the wrg underpinned by high precision 206pb 238u zircon dates from 15 volcanic tuffs including six tuffs previously dated using the 40ar 39ar technique weighted mean zircon 206pb 238u dates from this study are up to 1 0 myr younger than published anorthoclase and biotite 40ar 39ar data calibrated relative to fish canyon sanidine at 28 201 ma giving consideration to the complexities strengths and limitations associated with both the 40ar 39ar and 206pb 238u datasets our interpretation is that the recalculated 40ar 39ar dates are anomalously old and the 206pb 238u zircon dates more accurately constrain deposition 206pb 238u calibrated age depth models were developed in order to facilitate a robust intercomparison between marine and terrestrial archives of environmental change and indicate that i early orellan terrestrial cooling recorded at toadstool geologic park was synchronous with the onset of early oligocene antarctic glaciation and ii the last appearance datums of key chadronian mammal taxa are diachronous by ca 0 7 myr between central wyoming and nw nebraska

origin and causes of the mammoth steppe a story of cloud cover woolly mammal tooth pits buckles and inside out beringia to account for the vastness of the northern arid steppes during glacial episodes i propose the proximate key variable was simply frequent clear skies this hitherto under emphasized point is the hub which best explains many questions low maritime cloud cover best accounts for today s tundra and in a related way the cloudy polar front accounts for the whole of the taiga even during glacial maxima the proximity of the sea to the bering isthmus created intermittent maritime cloud cover this regional cloud cover produced an ecological interruption or buckle of the arid steppe belt while this beringian mesic buckle did not serve as an intercontinental ecological barrier to most steppe adapted species it does seem to have limited the distributions of woolly rhinos camels american kiangs short faced bears badgers and some others at the beginning of the holocene this narrow refugium seems to have been a source of some mesic adapted species which colonized westward into the now tundra vegetation of northern asia and eastward into northern north america this holocene expansion from a limited and regional pleistocene refugium created our present misconceptions about beringia the mid strait mesic ecological conditions were the exception to the more extensive arid adapted communities of the mammoth steppe 2000 published by elsevier science ltd all rights reserved

reducing disparity in radio isotopic and astrochronology based time scales of the late eocene and oligocene a significant discrepancy of up to 0 6 myr exists between radio isotopically calibrated and astronomically tuned time scales of the late eocene oligocene we explore the possible causes of this discrepancy through the acquisition of high precision 206pb 238u dating of zircons from 11 volcanic ash beds from the umbria marche sedimentary succession which hosts the global stratotype section and point for the base of the oligocene our results indicate that the four 40ar 39ar dates from the umbria marche succession which underpin the late eocene oligocene portion of the paleogene geomagnetic polarity time scale in the 2012 edition of the geological time scale are anomalously old by up to 0 5 myr conversely when integrated with the established magnetic polarity record of the umbria marche succession 206pb 238u zircon data from this study result in oligocene magnetic reversal ages that are generally equivalent to those obtained through the tuning of ocean drilling program odp site 1218 equatorial pacific furthermore our results indicate that the late eocene tuning of odp site 1218 and international ocean discovery program iodp sites u1333 1334 equatorial pacific to the 405 kyr eccentricity signal is accurate at least back to 36 ma propagating the full uncertainty of our radio isotopic data set and where appropriate taking into account locally derived astronomical time scales we arrive at an age of 34 09 0 08 ma for the eocene oligocene boundary and 28 11 0 17 ma for the base of the chattian

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

step wise change of asian interior climate preceding the eocene oligocene transition eot abstract understanding the global climate change from greenhouse to icehouse conditions at the eocene oligocene transition eot 34 million years ago requires climatic records from oceanic as well as continental realms of the key late eocene doubthouse period preceding this switch here we report integrated stratigraphic results from well dated late eocene continental mudflat to saline lake paleoenvironments of the xining basin northeastern tibetan plateau western china recording regional and global change cyclostratigraphic analysis strongly suggests continuous dominance of the 41 kyr obliquity cycle in the whole late eocene interval down to the base of polarity chron c18n 2n at 39 ma with additional input of the 100 kyr eccentricity cycle up to the base of chron c13r at 34 7 ma this might imply that high latitude climates dominated the area long before the eot probably related to incipient ice volume fluctuations furthermore our results reveal two paleoenvironmental deterioration steps preceding the eocene oligocene transition the first step occurs in the top of chron c17n 1n at 36 6 ma this age closely corresponds to 1 the high altitude pollen appearance in chron c16 2r at 36 4 ma in the same section 2 the recently dated final retreat of the tarim sea in western china and 3 a shift from precession to obliquity dominance in the atlantic ocean this near co occurrence suggests global change at this time we hypothesize this change is related to an increase in incipient ice sheet volume leading to passing threshold conditions for the high altitude pollen appearance and tarim sea retreat finally leading to decreased moisture availability in the xining basin at the second step in the base of chron c13r at 34 7 ma a substantial increase in clastic sedimentation rates is observed this might relate to increased climate variability preceding the greenhouse to icehouse transition at the eot that prevented landscapes to attain equilibrium configurations

age of eocene oligocene boundary based on extrapolation from north american microtektite layer microtektites believed to belong to the north american tektite strewn field have been found in upper eocene sediments in cores from nine deep sea drilling project sites in the caribbean sea gulf of mexico equatorial pacific and eastern equatorial indian ocean the microtektite layer has an age of 34 2 0 6 m y based on fission track dating of the microtektites and k ar and fission track dating of the north american tektites extrapolation from the microtektite layer to the overlying eocene oligocene boundary indicates an age of 32 3 0 9 m y for the eocene oligocene boundary as defined at each site in the initial reports of the deep sea drilling project this age is approximately 5 m y younger than the age of 37 5 m y that is generally assigned to the b undary based on recently published cenozoic time scales

lake level reconstruction and paleohydrology of birch lake central alaska based on seismic reflection profiles and core transects lake level history for birch lake alaska was reconstructed using seismic profiles and multiproxy sedimentary analyses including sedimentology geochemistry magnetic susceptibility and palynology twenty two seismic profiles 18 km total and eight sediment cores taken from the lake margin to its depocenter at 13 5 m provide evidence for low lake stands during the late pleistocene and holocene thirty one ams radiocarbon dates of macrofossils and pollen provide a century scale chronology prior to 12 700 14c yr b p the lake which now overflows was either seasonally dry or desiccated for prolonged periods indicating a severe period of aridity lake level rose more than 18 m between 12 700 and 12 200 14c yr b p before falling to 17 m below the level of overflow between 11 600 and 10 600 14c yr b p the water remained between 14 and 17 m below the overflow level onlap sedimentary sequences were formed during a transgression phase between 10 600 and 10 000 14c yr b p between 10 000 and about 8800 14c yr b p the lake was between 6 and 9 m below the overflow level lake level again rose approaching the overflow level between 8800 and 8000 14c yr b p seismic and core evidence of minor erosional events suggest lowstands of 2 6 m until 4800 14c yr b p there have been no prolonged periods of lake level depression since that time the major restructuring of the climate system during deglaciation evidently generated a complex set of fluctuations in effective moisture in interior alaska which likely affected eolian processes and vegetation development as well as lake levels

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

moraine chronosequence of the donnelly dome region alaska abstract we present 10be exposure ages from moraines in the delta river valley a reference locality for pleistocene glaciation in the northern alaska range the ages are from material deposited during the delta and donnelly glaciations which have been correlated with mis 6 and 2 respectively 10be chronology indicates that at least part of the delta moraine stabilized during mis 4 3 and that the donnelly moraine stabilized 17 ka these ages correlate with other dates from the alaska range and other regions in alaska suggesting synchronicity across beringia during pulses of late pleistocene glaciation several sample types were collected boulders single clasts and gravel samples amalgamated small clasts from around boulders as well as from surfaces devoid of boulders comparing 10be ages of these sample types reveals the influence of pre post depositional processes including boulder erosion boulder exhumation and moraine surface lowering these processes occur continuously but seem to accelerate during and immediately after successive glacial episodes the result is a multi peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly the absence of holocene ages implies relatively minor exhumation and or weathering since 12 ka

eocene oligocene paleoceanographic changes in the stratotype section massignano italy clues from rock magnetism and stable isotopes 1 we have conducted high resolution paleomagnetic and rock magnetic studies in addition to stable isotope analyses of the massignano sedimentary section which is the global stratotype section and point gssp for the eocene oligocene boundary our research builds upon the many past studies of the massignano section in seeking to understand the timing and nature of the paleoenvironmental variations that occurred during the transition for the earth s climate system from greenhouse to icehouse the new paleomagnetic results provide a refined magnetostratigraphy of the section and new age for the eocene oligocene boundary at 33 7 ma abrupt and large alternations in magnetic concentration composition and grain sizes that occur in the high resolution rock magnetic record are interpreted to be the result of rapid bimodal shifts in deep sea circulation that affect sediment sources or transport we speculate that currents flowing through the gateway between the atlantic and indo pacific oceans may have turned on and off as the gateway was progressively closing resulting in the deposition of two different assemblages of magnetic minerals at massignano finally stable isotope 18o and 13c data collected on ostracod valves also suggest significant changes in sea bottom circulation in the neo tethys ocean at and about 2 m y before the eocene oligocene boundary

towards a robust and consistent middle eocene astronomical timescale abstract until now the middle eocene has remained a poorly constrained interval of efforts to produce an astrochronological timescale for the entire cenozoic this has given rise to a so called eocene astronomical timescale gap vandenberghe et al 2012 a high resolution astrochronological calibration for this interval has proven to be difficult to realize mainly because carbonate rich deep marine sequences of this age are scarce in this paper we present records from middle eocene carbonate rich sequences from the north atlantic southeast newfoundland ridge iodp exp 342 sites u1408 and u1410 of which the cyclical sedimentary patterns allow for an orbital calibration of the geologic timescale between 38 and 48 ma these carbonate rich cyclic sediments at sites u1408 and u1410 were deposited as drift deposits and exhibit prominent lithological alternations couplets between greenish nannofossil rich clay and white nannofossil ooze the principal lithological couplet is driven by the obliquity of earth s axial tilt and the intensity of their expression is modulated by a cyclicity of about 173 kyr this cyclicity corresponds to the interference of secular frequencies s3 and s6 related to the precession of nodes of the earth and saturn respectively this 173 kyr obliquity amplitude modulation cycle is exceptionally well recorded in the xrf x ray fluorescence derived ca fe ratio in this work we first demonstrate the stability of the s3 s6 cycles using the latest astronomical solutions results show that this orbital component is stable back to at least 50 ma and can thus serve as a powerful geochronometer in the mid eocene portion of the cenozoic timescale we then exploit this potential by calibrating the geochronology of the recovered middle eocene timescale between magnetic polarity chrons c18n 1n and c21n comparison with previous timescales shows similarities but also notable differences in durations of certain magnetic polarity chrons we present a revision of previous astronomical timescales from the equatorial and south atlantic to overcome the differences between different mid eocene astrochronologies using our new records from the north atlantic combined with existing records from the south atlantic odp site 1263 and hole 702b and equatorial atlantic odp site 1260 we revise the durations of magnetic polarity chrons c18n 1n to c21n thereby arriving at a robust and self consistent closure of the middle eocene astronomical timescale gap

the early holocene milankovitch thermal maximum and humans adverse conditions for the denali complex of eastern beringia abstract calibration of 14c ages has forced the revision of paleoecological relationships with the milankovitch thermal maximum 10 000 9000 cal bp edwards and barker palaeogr palaeoclimatol palaeoecol 109 1994 127 in eastern beringia paleo geographic factors had dramatic consequences for humans many represented by the late pleistocene early holocene 13 000 7000 cal bp denali complex calibration of 71 radiocarbon ages associated with denali occupations indicates that the earliest precede both the milankovitch maximum and the spread of spruce in interior alaska by 2000 yr some denali occupations co occur with weakly developed forest soil horizons that reflect stabilized surfaces later capped by loess denali occupations peaked during the worldwide temperature decline between 8500 and 8000 cal bp the mesoglacial beget geology 11 1983 389 or the younger younger dryas fewer sites date to the milankovitch maximum and suggest an inverse relationship between warmer climate and human population

hydrogeochemistry of the campania region in southern italy abstract a geochemical study of thermal springs cold springs stream waters and natural gas emissions has been carried out in the campania region of southern italy this region hosts four quaternary volcanic areas and thermal springs and gas emissions occur in three of them most thermal springs discharge na cl composition waters of connate origin derived from post orogenic volcanic and sedimentary formations although high enthalpy systems are present in two of the four volcanic areas there appear to be no magmatic contributions to the thermal springs solute geothermometers are unreliable as spring waters are strongly affected by mixing with shallow brines before discharging thermal springs and gas emissions also occur in non volcanic areas where an extensive carbonate unit acts as a regional aquifer for cold low salinity bicarbonate waters thermal features in these areas occur in fractured zones associated with active faults their compositions are determined only by the type of rock encountered by solutions before surface discharge as in other areas of north central italy the widespread occurrence of hot and cold co2 rich springs and gas emissions in both volcanic and non volcanic zones suggests a deep origin for the co2

paleowind directions from the magnetic fabric of loess profiles in central alaska abstract two parallel profiles of alternating loess and paleosol horizons from the halfway house site west of fairbanks in central alaska were evaluated in terms of their potential for preserving paleowind directions combined the profiles span specmap marine oxygen isotope stages 1 6 approximately the last 150 ka our analytical tools consisted of measuring the sample s anisotropy of magnetic susceptibility and characterizing the magnetic mineralogy by multiple approaches both primary eolian and secondary reworked magnetic fabrics are recognized along certain intervals of both profiles primary eolian fabrics display a horizontal magnetic foliation and a well defined magnetic lineation corresponding to the paleodirection of sediment transport and deposition a systematic change in transport direction is observed where long term prevailing winds appear to shift from a nw se to n s direction during glacial and interglacial periods respectively

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

integrated stratigraphy of the oligocene pelagic sequence in the umbria marche basin northeastern apennines italy a potential global stratotype section and point gssp for the rupelian chattian boundary the oligocene represents an important time period from a wide range of perspectives and includes significant climatic and eustatic variations the pelagic succession of the umbria marche apennines central italy includes a complete and continuous sequence of marly limestones and marls with volcaniclastic layers that enable us to construct an integrated stratigraphic framework for this time period we present here a synthesis of detailed biostratigraphic magnetostratigraphic and chemostratigraphic studies along with geochronologic results from several biotite rich volcaniclastic layers which provide the means for an accurate and precise radiometric calibration of the oligocene time scale from this study the interpolated ages for the rupelian chattian stage boundary located in the upper half of chron 10n at meter level 188 in the monte cagnero section and corresponding to the o4 o5 planktonic foraminiferal zonal boundary are 28 36 ma paleomagnetic interpolation 28 27 0 1 ma direct radioisotopic dating and 27 99 ma astrochronological interpolation these ages appear to be slightly younger than those reported in recent chronostratigraphic time scale compilations the monte cagnero section is a potential candidate for defining the chattian global stratotype section and point gssp and some reliable criteria are here proposed for marking the rupelian chattian boundary according to international union of geological sciences iugs recommendations

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

radiometric time scale for the upper eocene and oligocene based on k ar and rb sr dating of volcanic biotites from the pelagic sequence of gubbio italy several samples of unaltered volcanic biotite were recovered from five biostratigraphically and magnetostratigaphically controlled bentonite horizons in the continuous upper eocene oligocene pelagic carbonate sequence of gubbio northern italy k ar and rb sr dates on these samples offer a unique opportunity to calibrate with closely spaced points the late paleogene biostratigraphic and magnetostratigraphic time scales until now time scales have been constructed by interpolating between less certain and more widely spaced data points our combined k ar and rb sr dates are here used to calibrate the following five stratigraphic levels from top to bottom level 5 upper part of globorotalia opima opima planktonic foraminiferal zone upper part of indistinct np23 np24 nannoplankton zone and cp18 nannoplankton zone bottom of magnetic anomaly 9n 28 0 0 3 ma level 4 globigerina ampliapertura and cassigerinella chipolensis zone lower part of np23 zone and bottom of cp18 zone upper part of anomaly 12r 32 0 0 8 ma level 3 pseudohastigerina micra zone upper part of np21 and cp16b zones top of anomaly 13n 35 4 0 4 ma level 2 upper part of globigerinatheka semiinvoluta zone upper part of np18 and cp15a zones top of magnetic anomaly 16n 36 0 0 4 ma level 1 lower part of g semiinvoluta zone between zones np18 and np19 middle part of zone cp15a upper part of anomaly 17n 36 4 0 3 ma from these data the interpolated age for the much debated eocene oligocene boundary is 35 7 ma with a 2 standard deviation uncertainty of 0 4 ma

the rosa keystone dunes field the geoarchaeology and paleoecology of a late quaternary stabilized dune field in eastern beringia stabilized sand sheets and dunes hold a remarkable amount of information on paleoenvironmental conditions under which late quaternary landscapes evolved in northern subarctic regions we provide the results of a project focused on understanding the development of lowland environments and ecosystems including dunes and sand sheets which were critical habitat for early human occupations in subarctic regions our study area is the rosa keystone dunes field in the shaw creek flats of the middle tanana river basin interior alaska one of the oldest continuously occupied areas in north america 14 000 cal bp to present the disturbance regimes of reactivated dunes and associated forest fire cycles between 12 500 and 8800 cal bp fostered a unique early to mid successional mixed vegetation community including herbaceous tundra shrubs and deciduous trees this environment provided key habitats for large grazers and browsers significant resources for early hunter gatherer populations in central alaska aft

optical dating of holocene sediments from a variety of geomorphic settings using single grains of quartz this paper presents an improved method for the optical dating of holocene sediments from a variety of geomorphic settings we have measured the equivalent dose de in individual grains of quartz using green laser light for optical stimulation and have simulated the de distributions for multiple grain synthetic aliquots using the single grain data for 12 samples of known independent age we show that application of a minimum age model to the single grain and small 10 grain aliquot de data provides the most accurate estimate of the burial dose for nine of the samples examined 3 aeolian 5 fluvial and 1 marine the weighted mean de as obtained using the central age model gives rise to burial age overestimates of up to a factor of 10 for these nine samples whether single grains small aliquots or large 100 grain aliquots are used for the other three samples two aeolian and one fluvial application of either the minimum age model or the central age model to the single grain small aliquot and large aliquot de data yields burial ages in accord with the independent age control we infer that these three samples were well bleached at the time of deposition these results show that heterogeneous bleaching of the optical dating signal is commonplace in nature and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition we also show that grains sensitive to infrared ir stimulation can give rise to low de values which will result in significant underestimation of the burial dose and hence of the age of deposition we demonstrate that use of a modified single aliquot regenerative dose protocol incorporating ir stimulation prior to green light stimulation deals effectively with contamination by ir sensitive grains we conclude that application of the modified protocol to single grains or small aliquots of quartz using the lowest de population to estimate the burial dose is the best means of obtaining reliable ages for holocene sediments from a wide range of depositional environments d 2003 elsevier b v all rights reserved

extinction and environmental change across the eocene oligocene boundary in tanzania the eocene oligocene transition between ca 34 and 33 5 ma is the most profound episode of lasting global change to have occurred since the end of the cretaceous diverse geological evidence from around the world indicates cooling ice growth sea level fall and accelerated extinction at this time turnover in the oceanic plankton included the extinction of the foraminifer family hantkeninidae which marks the eocene oligocene boundary in its type section another prominent extinction affected larger foraminifera which resulted in the loss of some of the world s most abundant and widespread shallow water carbonate secreting organisms however problems of correlation have made it difficult to relate these events to each other and to the global climate transition as widely recorded in oxygen and carbon isotope records from deep sea cores here we report new paleontological and geochemical data from hemipelagic sediment cores on the african margin of the indian ocean tanzania drilling project sites 11 12 and 17 the eocene oligocene boundary is located between two principal steps in the stable isotope records the extinction of shallow water carbonate producers coincided with an extended phase of ecological disruption in the plankton and preceded maximum glacial conditions in the early oligocene by 200 k y

paleopedology of the chadron formation of northwestern nebraska implications for paleoclimatic change in the north american midcontinent across the eocene oligocene boundary abstract the big cottonwood creek member is a newly recognized lithostratigraphic unit of the chadron formation of northwestern nebraska i measured 23 superimposed paleosol profiles within 29 m of strata exposed 0 4 km 0 25 mile east of the type section of the big cottonwood creek member at toadstool park in northwestern nebraska and recognized four main types of paleosols the paleosols are all well drained moderately alkaline to alkaline oxidized and range from weakly developed azonal ustifluvents to moderately and well developed paleustalfs and argiustolls with argillic and petrocalcic horizons based on changes in soil structure horizons root traces and geochemical trends these paleosols record a gradual change from humid forested conditions of the late eocene to more seasonal semi arid open range conditions leading up to the global climatic deterioration event of the early oligocene at 33 2 ma this interpretation is supported by associated changes in sedimentology fluvial architecture floras and faunas over this period of time the section at toadstool park is significant in that it establishes a link between the big badlands of south dakota and correlative deposits of wyoming the contact of the chadron and brule formations in the big badlands of south dakota is marked by an unconformity that is in part correlative to the earliest oligocene sediments that elsewhere record the global climatic deterioration event at 33 2 ma the paleosols of the big cottonwood creek member of northwestern nebraska fill in a significant part of this gap and record paleoclimatic conditions of the late eocene leading up to the global climatic deterioration event of the early oligocene using the latest lithostratigraphic biostratigraphic magnetostratigraphic and tephrostratigraphic data for the white river group this change to more arid conditions in the midcontinent appears to have progressed from west to east over time

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

geochemical evidence for the origin of late quaternary loess in central alaska loess is extensive in central alaska but there are uncertainties about its source and the direction of paleo winds that deposited it both northerly and southerly winds have been inferred the most likely sources of loess are the tanana river south the nenana river southeast and the yukon river north late quaternary loess in central alaska has immobile trace element compositions cr sc th ta th sc th u eu eu gdn ybn that indicate derivation mostly from the tanana river however other ratios as sb zr hf lan ybn and quantitative modeling indicate that the yukon river was also a source during the last glacial period there may have been a longer residence time of the siberian and canadian high pressure cells along with a strengthened aleutian low pressure cell this would have generated regional scale northeasterly winds and explains derivation of loess from the yukon river however superim posed upon this synoptic scale circulation there may have been strong southerly katabatic winds from expanded glaciers on the northern flank of the alaska range these winds could have provided eolian silt from the tanana river yukon river and tanana river sediments are highly calcareous whereas fairbanks area loess is not this suggests that carbonate leaching in loess kept ahead of sedimentation and that late quaternary loess in central alaska was deposited relatively

holocene history of the great kobuk sand dunes northwestern alaska abstract located just north of the arctic circle the great kobuk sand dunes gksd are an inland dune field that is closely surrounded by boreal forest the history of the gksd tells us about changes in aridity a climatic parameter whose history is poorly understood at high latitudes vegetated dunes in several states of geomorphic preservation surround the active dune field today evidencing a complex history of holocene activity small lakes in the forest bordering the dunes accumulate wind blown sand we use 14 c dated lake sediment cores to reconstruct a continuous history of sand influx over the last 8000 yr the validity of this record is supported by limiting ages obtained from stratigraphic sections within the dune field the extent of the gksd underwent a fluctuating shrinkage coincident with neoglaciation this downsizing trend was interrupted by periods of increased sand deposition into lakes occurring 4800 4200 3300 2600 1300 700 and 300 100 calendar years ago aridity in the kobuk valley during the holocene probably was controlled by the frequency of north pacific storms entering the region in late summer our results describe the first continuous history of changing moisture balance for central beringia during the holocene and comprise a baseline against which future records of climatic and ecological change in this region can be compared

eolian deflation by ancient katabatic winds a late quaternary example from the north alaska range strong katabatic winds are frequently generated in glaciated mountain valleys of the alaska range by downglacier gravitational flow of chilled air stronger katabatic winds probably occurred during late quaternary time when glaciers were more extensive and such winds may have greatly influenced eolian sedimentation in nenana river valley and in most of adjacent teklanika river valley the entire 1 to 2 m thick eolian cap is postglacial in age and the beginning of loess deposition coincides almost exactly with rapid recession of late wisconsin ice previously deposited loess and bluff edge dunes were apparently deflated during the last glaciation between 25 000 and 12 000 yr b p loess deposition in these mountain valleys thus is exclusively an interglacial phenomenon glacial phases are characterized by deflation meteorological modeling of katabatic winds generated during the last glaciation predicts that paleowind velocities greatly exceeded the entrainment thresholds required for eolian deflation when both nenana river and teklanika river valleys are compared theoretical differences in the potential for generating katabatic winds and differences in valley physiography explain why pre holocene loess is preserved in downstream reaches of teklanika river valley and not nenana river valley the presence of strong katabatic winds in mountain valleys beyond former glacier limits has significant implications for late pleistocene paleoecology and archeology

geothermometry on fluids circulating in a carbonate reservoir in north central italy the peri tyrrhenian belt of north central italy is a site of large scale fluid circulation in mesozoic carbonate anhydritic formations of thermal waters with ca sulfate composition these carbonate formations are the principal geothermal reservoir of the known italian geothermal fields owing to differences in the regional structure these carbonate rocks may have an intrinsic high or low hydraulic continuity the ca sulfate springs that surface at the periphery of these formations have circulated in the unconfined parts of the carbonate aquifer the high salinity na chloride geothermal fluids discharge from the confined parts of the same reservoir rocks these fluids are somewhat separated from fluids generated in the unconfined parts by possible barriers of low permeability they are also diluted with the ca sulfate waters and have re equilibrated at lower temperature because of these conditions the assessment of the deep reservoir temperatures cannot be made using rapidly re equilibrating geothermometers such as the sio2 geothermometer the latter reveals the temperature of the unconfined aquifer at best the study of the geohydrological nature of the reservoir rocks the composition of liquid and gas phases and the statistical behavior of the main chemical geothermometers applied to the shallow cold waters of the principal italian geothermal areas has shown that the geothermometer based on nali ratio seems to be the most reliable to evaluate the deep temperatures inside the confined parts of the carbonate reservoir

macrofossil and pollen evidence for full glacial steppe within an ecological mosaic along the bluefish river eastern beringia abstract plant and insect macrofossil assemblages dating to the full glacial late wisconsinan are rare from eastern beringia here we present an assemblage of fossil pollen insect and plant macrofossils recovered from alluvium at the bluefish exposure northern yukon territory nine ams radiocarbon ages place these data between ca 18 880 16 440 14c yr bp 22 313 19 597 cal yr bp these data indicate that xeric steppe rich in bunchgrasses poa and elymus artemisia frigida and diverse forbs was interspersed within a mosaic of local vegetation types including mid rich fens mesic graminoid meadows steppe tundra and herb tundra macrofossils and minor pollen of tundra forbs suggest steppe tundra plant associations within midslope elevations and discontinuous herb tundra on high elevation uplands on exposed bedrock ridges the composition and distribution of local vegetation was dependent on available moisture drainage aspect and elevation compositional and physiognomic similarities can be made with extrazonal steppe dominated dry slopes and high elevation steppe tundra ecotones in central alaska and yukon territory our paleoecological data reflect environments inhabited by the diverse late pleistocene bluefish caves fauna including woolly mammoth horse steppe bison and saiga antelope

the irpinia italy 1980 earthquake detailed analysis of a complex normal faulting a detailed analysis of near source strong motion and leveling data together with the results of teleseismic waveform modeling by westaway and jackson 1987 and aftershock studies by deschamps and king 1984 allows a satisfactory kinematic description of the complex normal faulting associated with the magnitude ms 6 9 november 23 1980 irpinia earthquake southern italy the three main rupture episodes starting at about 0 20 and 40 s are here associated with better constrained source parameters than in previous studies we first evaluated the triggering time for the 11 closest accelerometers by using the well recorded 40 s strong motion phases this gave the absolute time and location of the dominant episodes of faulting the first rupture propagated mainly toward the northwest on a ne dipping normal fault at a mean velocity close to 3 km s for about 20 km and continued 15 km further on smaller subfaults it was associated with surface breakage in the southeastern part the second rupture started from the southeastern end of the first rupture about 18 s after it and propagated about 20 km toward the southeast on a low angle normal fault dipping 20 ne it was associated with secondary faulting on steeper planes reaching the surface the third and last episode at 39 s nucleated near the first hypocenter at shallower depth and the rupture possibly propagated on a 10 to 15 km long normal fault striking se antithetic to the first activated fault a clear correlation appears between the strength of the geological formations and the existence of surface breakage and shallow aftershock activity

dune stabilization in central and southern yukon in relation to early holocene environmental change northwestern north america abstract eolian deposits of central and southern yukon northwestern canada consist of loess mantles small areas of active dunes and larger stabilized dune fields dune fields in valley settings within the region are situated both within and beyond the limit of the last glaciation infrared stimulation luminescence irsl dating in central and southern yukon reveals that these dune fields stabilized as late as 9 8 5 ka well after the retreat of cordilleran glaciers these findings are comparable to other valley setting dune fields and loess from central alaska which record activity during the period from the lateglacial to the holocene thermal maximum htm and reduced or altered activity after 9 8 ka post glacial dune activity was most likely related to warm dry conditions during the htm under predominantly shrub tundra vegetation early holocene stabilization of these dunes probably occurred in response to cooler moister conditions and replacement of predominantly tundra by boreal forest cover dominated by spruce stabilization of dune fields in southern yukon and alaska most likely represented an extension of the time transgressive stabilization of dune fields that occurred across northwestern north america with the post glacial expansion of the boreal forest

applying luminescence dating of ceramics to the problem of dating arctic archaeological sites abstract dating arctic archaeological sites is challenging because of limited terrestrial bone and the high probability of old wood in northern regions luminescence dating of ceramic materials abundant in western arctic late holocene archaeological sites offers another potential source of chronological information we set out to evaluate whether luminescence can provide chronological information in one particular region we obtained luminescence ages on 14 pottery samples from seven study sites located on the coast and interior regions of northwest alaska twelve of the luminescence dates are in accord with radiocarbon tree ring and artifact data from the study sites results indicate that all of the study sites may be older than previously established suggesting previously unknown early thule or birnirk occupation of the coast and interior of northwest alaska we conclude that luminescence dating of ceramic materials from this region is possible and can complement other dating methods that are more widely accepted in the western arctic there is considerable potential through future applications of luminescence dating for improving northeast asian and arctic chronologies and expanding our understanding of circumpolar holocene migration cultural interaction and change

the role of mantle co2 in volcanism abstract carbon dioxide is the propellant gas in volcanic eruptions and is also found in mantle xenoliths it is speculated that co 2 occurs as a free gas phase in the mantle because there is no reason to expect co 2 to be so universally associated with volcanic rocks unless the co 2 comes from the same source as the volcanic rocks and their xenoliths if correct the presence of a free gas in the mantle would lead to physical instability with excess gas pressure providing the cause of both buoyancy of volcanic melts and seismicity in volcanic regions convection in the mantle and episodic volcanic eruptions are likely necessary consequences this suggestion has considerable implications for those responsible for providing warnings of impending disasters resulting from volcanic eruptions and earthquakes in volcanic regions

variation in radiocarbon ages of soil organic matter fractions from late quaternary buried soils radiocarbon dating of three organic matter fractions total humic acid and residue isolated from late quaternary buried soils of the central great plains reveals that there often are considerable differences among but no consistent order to the ages of fractions for late holocene soils the residue fraction or the total fraction generally produces the oldest age for late pleistocene soils however no fraction was consistently the oldest the absence of a consistent sequence of fraction ages is attributed to postburial contamination of soils when bulk samples from the same soil were split and sent to two laboratories different radiocarbon ages were usually obtained the variability in radiocarbon ages of soil organic matter confirms that caution should be taken when using radiocarbon ages obtained from different laboratories to make regional stratigraphic correlations

a 31 000 year record of paleoenvironmental and lake level change from harding lake alaska usa physical and geochemical proxy analyses of sediment cores from harding lake in central alaska are used to reconstruct paleoenvironmental change and millennial scale fluctuations in lake level for the last similar to 31 000 years we analyzed a composite 422 cm core from the lake depocenter 42 1 m water depth and identified 4 distinct lithologic units based on variability in dry bulk density organic matter biogenic silica carbon to nitrogen mass ratios c n organic matter carbon isotopes delta c 13 pollen and elemental abundances via scanning x ray fluorescence with age control provided by 16 accelerator mass spectrometry radiocarbon dates and pb 210 dating in addition we analyzed a transect of cores from 7 1 m 10 75 m 15 91 m and 38 05 m water depths to identify lake level fluctuations and to characterize sediment compositional changes as a function of water depth organic matter content and magnetic susceptibility values in surface sediments from all transect cores show a strong correlation with water depth interpretation of four lithologic units with well dated contacts produced a record of water depth variations that is consistent with independent climate records from eastern beringia basal coarse grained sediments quartz pebble diamicton were deposited prior to 30 700 calendar years before present yr bp possibly from fluvial reworking or deflation during a period of severe aridity unit 1 sediments were deposited between 30 700 and 15 700 yr bp and are characterized by a low organic matter content a high magnetic susceptibility and low biogenic silica concentrations resulting from very low lake levels low terrestrial and in lake productivity and a high flux of clastic sediment an abrupt increase in organic matter and biogenic silica concentration marks the transition into unit 2 sediments which were deposited between 15 700 and 9 400 yr bp when lake levels were higher and variable relative to unit 1 the transition to full interglacial conditions at 9 400 yr bp marks the beginning of unit 3 here an abrupt increase in the sedimentation rate organic matter and biogenic silica concentration occurs along with a corresponding decrease to low magnetic susceptibility these high values persist until 8 700 yr bp signifying a rapid rise to higher lake levels in comparison to units 1 and 2 unit 4 sediments were deposited between 8 700 yr bp to 2010 ad and generally contain high concentrations of organic matter and biogenic silica with low magnetic susceptibility suggesting that lake levels were relatively high and stable during the middle to late holocene c 2014 elsevier ltd all rights reserved

late pleistocene paleoecology of arctic ground squirrel urocitellus parryii caches and nests from interior alaska s mammoth steppe ecosystem usa botanical analyses of fossil and modern arctic ground squirrel urocitellus parryii caches and nests have been used to reconstruct the past vegetation from some parts of beringia but such archives are understudied in alaska five modern and four fossil samples from arctic ground squirrel caches and nests provide information on late pleistocene vegetation in eastern beringia modern arctic ground squirrel caches from alaska s arctic tundra were dominated by willow and grass leaves and grass seeds and bearberries which were widespread in the local vegetation as confirmed by vegetation surveys late pleistocene caches from interior alaska were primarily composed of steppe and dry tundra graminoid and herb seeds graminoid cuticle analysis of fossil leaves identified calamagrostis canadensis koeleria sp and carex albonigra as being common in the fossil samples stable carbon isotopes analysis of these graminoid specimens indicated that plants using the c3 photosynthetic pathways were present and functioning with medium to high water use efficiency fossil plant taxa and environments from ground squirrel caches in alaska are similar to other macrofossil assemblages from the yukon territory which supports the existence of a widespread mammoth steppe ecosystem type in eastern beringia that persisted throughout much of the late pleistocene

pleistocene graminoid dominated ecosystems in the arctic abstract we review evidence obtained from analyses of multiple proxies floristics mammal remains paleoinsects pollen macrofossils plant cuticles phytoliths stable isotopes and modeling that elucidate the composition and character of the graminoid dominated ecosystems of the pleistocene arctic the past thirty years have seen a renewed interest in this now extinct biome sometimes referred to as tundra steppe steppe tundra in north american sources while many questions remain converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the arctic confirming earlier conjectures completed in the 1960s 1980s a variety of still existing species of grasses and forbs played key roles in the species assemblages of the time but their mixtures were not analogous to the tundras of today local mosaics based on topography proximity to the ice sheets and coasts soil heterogeneity animal disturbance and fire regimes were undoubtedly present however inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity these past ecosystems were maintained by a combination of dry and cold climate and grazing pressure disturbance by large e g mammoth and horse and small e g ground squirrels mammals some recent studies from eastern beringia alaska suggest that more progress will be possible when analyses of many proxies are combined at local scales

vertebrate tracks in pleistocene eolian sand sheet deposits of alaska abstract deformation structures interpreted as vertebrate hoof and foot tracks occur within upper pleistocene eolian sand sheet deposits in the stabilized kantishna sand sea of central alaska and in the nushagak lowland of southwestern alaska exposures of tracks are generally limited to cross sections which reveal concave up deformation structures in which displacement of preexisting strata diminishes downward deposits in both areas contain tracks that are 6 to 16 cm in diameter and are divided by a central ridge reflecting formation by artiodactyl even toed ungulates larger 21 34 cm tracks without a central ridge observed in the nushagak lowland were formed by proboscideans probably woolly mammoth large vertebrate tracks occur within irregularly stratified sand and silty sand that accumulated upon partially vegetated sand sheets and within thin even wind ripple laminae of unvegetated sand sheets the presence of tracks at multiple stratigraphic levels and preservation of roots and rhizocretions within the eolian deposits suggest that vegetated sand sheets may have formed a locally important grazing habitat for large herbivores during at least part of the last glaciation recognition that vertebrate tracks are preserved in eolian sand sheet deposits and in deposits of other environments as well opens a new source of stratigraphic and paleoecological data to aid reconstruction of the vanished ecosystems of beringia

calibration of the latest eocene oligocene geomagnetic polarity time scale using 40ar 39ar dated ignimbrites a discontinuous record of late eocene oligocene geomagnetic polarity has been determined using high precision 0 15 m y 40ar 39ar sanidine dating and a paleomagnetic study of 37 27 ma ignimbrites in new mexico colorado and texas this record provides age control for several geomagnetic polarity reversals that occurred during three periods of intense ignimbrite volcanism 36 8 33 5 ma 32 7 31 4 ma 29 1 26 9 ma the relative timing of these polarity reversals permits four possible correlations with the geomagnetic polarity time scale gpts the preferred correlation yields calibration ages for chron c10r 28 0 29 0 ma and chron c13r 34 4 33 1 ma that indicate an eocene oligocene boundary age near 33 4 ma some 0 3 0 6 m y younger than boundary ages indicated by other recently proposed gpts calibrations based on terrestrial and marine sedimentary sequences

astronomic calibration of the late oligocene through early miocene geomagnetic polarity time scale at ocean drilling program odp site 1090 subantarctic south atlantic benthic foraminiferal stable isotope data from cibicidoides and oridorsalis span the late oligocene through early miocene f24 16 ma at a temporal resolution of f5 ky over the same interval a magnetic polarity stratigraphy can be unequivocally correlated to the geomagnetic polarity time scale gpts thereby providing direct correlation of the isotope record to the gpts in an initial age model we use the newly derived age of the oligocene miocene o m boundary of 23 0 ma of shackleton et al geology 28 2000 447 revised to the new astronomical calculation la2003 of laskar et al icarus in press to recalculate the spline ages of cande and kent j geophys res 100 1995 6093 we then tune the site 1090 y 18 o record to obliquity using la2003 in this manner we are able to refine the ages of polarity chrons c7n through c5cn 1n the new age model is consistent within one obliquity cycle with previously tuned ages for polarity chrons c7n through c6bn from shackleton et al geology 28 447 450 2000 when rescaled to la2003 the results from site 1090 provide independent evidence for the revised age of the oligocene miocene boundary of 23 0 ma for early miocene polarity chrons c6aar through c5cn our obliquity scale age model is the first to allow a direct calibration to the gpts the new ages are generally within one obliquity cycle of those obtained by rescaling the cande and kent j geophys res 100 1995 6093 interpolation using the new age of the o m boundary 23 0 ma and the

late pleistocene and holocene glaciation of the fish lake valley northeastern alaska range alaska we reconstructed a chronology of glaciation spanning from the late pleistocene through the late holocene for fish lake valley in the north eastern alaska range using 10 be surface exposure dating and lichenometry after it attained its maximum late wisconsin extent the fish lake valley glacier began to retreat ca 16 5 ka and then experienced a readvance or standstill at 11 6 0 3 ka evidence of the earliest holocene glacial activity in the valley is a moraine immediately in front of little ice age lia moraines and is dated to 3 3 3 0 ka a subsequent advance culminated at ca ad 610 900 and several lia moraine crests date to ad 1290 1640 1860 and 1910 our results indicate that 10 be dating from high elevation sites can be used to help constrain late holocene glacial histories in alaska even when other dating techniques are unavailable close agreement between 10 be and lichenometric ages reveal that 10 be ages on late holocene moraines may