freshwater control of ice rafted debris in the last glacial period at mono lake california usa abstract the type section silts of the late pleistocene wilson creek formation at mono lake contain outsized clasts dominantly well rounded pebbles and cobbles of sierran lithologies lithic grains 425 m show a similar pattern of variability as the 10 mm clasts visible in the type section with decreasing absolute abundance in southern and eastern outcrops the largest concentrations of ice rafted debris ird occur at 67 57 ka and 46 32 ka with strong millennial scale variability while little ird is found during the last glacial maximum and deglaciation stratigraphic evidence for high lake level during high ird intervals and a lack of geomorphic evidence for coincidence of lake and glaciers strongly suggests that rafting was by shore ice rather than icebergs correspondence of carbonate flux and ird implies that both were mainly controlled by freshwater input rather than disparate non climatic controls conversely the lack of ird during the last glacial maximum and deglacial highstands may relate to secondary controls such as perennial ice cover or sediment supply high ird at mono lake corresponds to low glacial flour flux in owens lake both correlative to high warm season insolation high resolution extra basinal correlation of the millennial peaks awaits greatly improved age models for both records

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

amino acid estimates of latitudinal temperature gradients and geochronology of loess deposition during the last glaciation mississippi valley united states principles of amino acid paleothermometry are used to estimate paleotemperatures and latitudinal temperature gradients for the period during and following the last glacial maximum in the mississippi valley gastropod shells were collected from the peoria loess for amino acid analysis and arrhenius parameters of isoleucine epimerization were determined experimentally for the gastropod genera catinella and hendersonia there are 37 radiocarbon and 5 thermoluminescence ages that constrain the paleotemperature estimates and provide additional chronological data for loess deposition in the region amino acid paleotemperature estimates suggest that the north south temperature gradient was significantly depressed in the mississippi valley for a considerable period during the past 25 k y effective diagenetic temperature estimates indicate that at some time during or following the last glaciation the effective temperature gradient was 0 3 0 6 c degree of latitude which is significantly lower than the modern mean annual air temperature gradient of 0 9 c degree of latitude calculated effective paleotemperatures for three localities in tennessee and mississippi suggest that temperatures were 7 13 c lower than present during the period from ca 24 to 16 ka in the lower mississippi valley these results provide additional evidence for a significant cooling in southern united states continental temperatures during the last glacial maximum

the changing nature of mantle hotspots through time implications for the chemical evolution of the mantle the melting products of mantle plumes can place constraints on the geochemical structure of the mantle and show how it has varied through time the highest temperature melts komatiites and picrites derived from each plume are assumed to represent the best available sample of the thermal boundary layer from which the plume originates a survey of the geochemistry of picrites and komatiites shows that they underwent a fundamental change at about the archean proterozoic boundary archean komatiites have depleted or neutral geochemistry whereas most protero zoic and younger picrites have originated from enriched oib type mantle although rare depleted plumes persist to the tertiary e g gorgona if plumes originate from a thermal boundary layer near the core mantle interface the composition of this layer must have changed from a mixture of depleted and neutral mantle during the archean to mainly enriched mantle in the proterozoic this change coincides with a drop in the maximum mgo content of the ma

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

cosmogenic 10be and 36cl ages from late pleistocene terminal moraine complexes in the taylor river drainage basin central colorado usa abstract cosmogenic surface exposure ages from boulders on a terminal moraine complex establish the timing of the local last glacial maximum lgm in the taylor river drainage basin central colorado five zero erosion 10 be ages have a mean of 19 5 1 8 ka while that for three 36 cl ages is 20 7 2 3 ka corrections for modest rates 1 mm ka 1 of boulder surface erosion result in individual and mean ages that are generally within 2 of their zero erosion values both the means and the range in ages of individual boulders are consistent with those reported for late pleistocene moraines elsewhere in the southern and middle rocky mountains and thus suggest local lgm glacier activity was regionally synchronous two anomalously young zero erosion 10 be ages mean 14 4 0 8 ka from a second terminal moraine are tentatively attributed to the boulders having been melted out during a late phase of ice stagnation

climatic controls of western u s glaciers at the last glacial maximum abstract we use a nested atmospheric modeling strategy to simulate precipitation and temperature of the western united states 18 000 years ago 18 ka the high resolution of the nested model allows us to isolate the regional structure of summer temperature and winter precipitation that is crucial to determination of the net mass balance of late pleistocene mountain glaciers in this region of diverse topography and climate modeling results suggest that climatic controls of these glaciers varied significantly over the western u s glaciers in the northern rocky mountains existed under relatively cold july temperatures and low winter accumulation reflecting anticyclonic easterly wind flow off the laurentide ice sheet in contrast glaciers that existed under relatively warmer and wetter conditions are located along the pacific coast south of oregon where enhanced westerlies delivered higher precipitation than at present between these two groupings lie glaciers that were controlled by a mix of cold and wet conditions attributed to the convergence of cold air from the ice sheet and moisture derived from the westerlies sensitivity tests suggest that for our simulated 18 ka climate many of the glaciers exhibit a variable response to climate but were generally more sensitive to changes in temperature than to changes in precipitation particularly those glaciers in central idaho and the yellowstone plateau our results support arguments that temperature depression generally played a larger role in lowering equilibrium line altitudes in the western u s during the last glacial maximum than did increased precipitation although the magnitude of temperature depression required for steady state mass balance varied from 8 18 c only the sierra nevada glaciers required a substantial increase in precipitation to achieve steady state mass balance while glaciers in the cascade range existed with decreased precipitation

bar development in a fluvial sandstone westphalian a scotland the fluvial sandstone beneath the mill coal in the westphalian a of scotland erosively overlies a lake mudstone slightly erosive surfaces within the sandstone traceable for over 200 m are used to divide it into two types of major sedimentary units termed type a and type b type a sand units are approximately 200 m wide up to 7 m thick convex upward and lenticular in all directions the constituent cosets overlap to the ene and dip mainly at 1 2 downcurrent nnw but locally at 10 15 where thickest type a sand units display a vertical facies sequence commencing with trough cross bedded and massive sandstone overlain by a thick zone of ripple cross lamination a thin zone of trough cross beds and a variably eroded silt drape up to 0 4 m thick attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation type a sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events the bar is thought to have had a similar topographic significance to sand waves described from the brahmaputra and slip face bounded bars observed in the south saskatchewan river palaeocurrents measured from trough cross bed sets 0 3 1 0 m thick within type b sand units indicate flow to the wsw perpendicular to the palaeoflow direction measured from type a units in sections perpendicular to the wsw flow direction type b units are lenticular and in ene wsw trending sections they can be traced for over 80 m at a constant thickness type b sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops the sandstone described herein is interpreted as a braided type river deposit but is atypical because it is fine grained and has an internal structure dominated by ripple cross lamination and upper phase plane beds the palaeoriver is thought to have been of low sinuosity 7 10 m deep with a high suspended load and large rapidly fluctuating discharge at low stage a braided type flow pattern developed around submerged bars the regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

late pleistocene glaciations in the northwestern sierra nevada california pleistocene fluvial landforms and riparian ecosystems in central california responded to climate changes in the sierra nevada yet the glacial history of the western sierra remains largely unknown three glacial stages in the northwestern sierra nevada are documented by field mapping and cosmogenic radionuclide surface exposure crse ages two crse ages of erratic boulders on an isolated till above bear valley provide a limiting minimum age of 76 400 3800 10be yr another boulder age provides a limiting minimum age of 48 800 3200 10be yr for a broad crested moraine ridge within bear valley three crse ages producing an average age of 18 600 1180 yr were drawn from two boulders near a sharp crested bouldery lateral moraine that represents an extensive tioga glaciation in bear valley nine crse ages from striated bedrock along a steep valley transect average 14 100 1500 yr and suggest rapid late glacial ice retreat from lower fordyce canyon with no subsequent extensive glaciations these ages are generally consistent with glacial and pluvial records in east central california and nevada

pacing the post last glacial maximum demise of the animas valley glacier and the san juan mountain ice cap colorado during the last glacial maximum lgm a 5000 km 2 ice cap covered the san juan mountains of southwest colorado the largest valley glacier draining this ice cap occupied the animas valley and flowed 91 km to the south to characterize the post lgm demise of the animas valley glacier we employ cosmogenic 10 be to date the lgm terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples the 10 be depth profile within the terrace sediments suggests abandonment at 19 4 1 5 ka as deglaciation began the ponding of glacial lake durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment the age of the terrace therefore records the initiation of lgm retreat negligible 10 be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory glacial polish exposure ages monotonically decrease up valley from 17 1 to 12 3 ka with the single exception of a sample collected from a quartzite rib yielding an average retreat rate of 15 4 m yr this trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history retreat of the animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes deglaciation lasted for 7 2 k y and was complete by 12 3 1 0 ka the retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying

wisconsin glaciation of the sierra nevada 79 000 15 000 yr b p as recorded by rock flour in sediments of owens lake california chemical analyses of the clay sized fractions of 564 continuous sediment samples 200 yr resolution from composite core ol90 92 allow quantification of an abundance of glacial rock flour rock flour produced during glacier advances is represented by clay sized plagioclase k feldspar and biotite in homogeneous internal composition the abundance of rock flour is deemed proportional to the intensity of glacies advances age control for the composite section is provided by combining previously published radiocarbon dates on organics u th dates on ostracode shells and u th dates on saline minerals from nearby searles lake correlated to ol92 by pollen the rock flour record displays three levels of variability 1 a dominant one of about 20 000 yr related to summer insolation and precipitation 2 an intermediate one of 3000 5000 yr perhaps related to north atlantic heinrich events and 3 a minor one of 1000 2000 yr perhaps related to north atlantic thermohaline driven air temperature variation

correlation of late pleistocene glaciation in the western united states with north atlantic heinrich events a survey of the chronology of late pleistocene glaciers in the western united states indicates a record of glacier advances during the last glaciation which is more variable than that predicted by orbital forcing numerical dating of late pleistocene deposits from the puget lobe of the cordilleran ice sheet and alpine glaciers and ice caps in the rocky mountains and cascade range suggests that advances and retreats of these glaciers were in phase with episodes of growth and collapse of the laurentide ice sheet associated with the north atlantic heinrich events specifically the existing chronologies indicate that these glaciers were advancing to their terminal areas up to several thousand years before a heinrich event and retreated shortly thereafter because midlatitude glaciers respond relatively rapidly to climate change this complex record of glacial fluctuations suggests mechanisms of climate forcing in western north america that are in some way tied to heinrich events one possible mechanism involves southerly and northerly displacement of the jet stream across the western united states in response to growth and collapse of the laurentide ice sheet

small valley glaciers and the effectiveness of the glacial buzzsaw in the northern basin and range usa the glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens studies to date have largely focussed on regions where large glaciers tens of kilometres long have been active in light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions four ranges in the northern basin and range idaho montana and wyoming usa were chosen for this analysis estimates of maximum pleistocene slip rates along normal faults bounding the beaverhead bitterroot mountains similar to 0 14 mm y 1 lemhi range similar to 0 3 mm y 1 and lost river range similar to 0 3 mm y 1 are an order of magnitude lower than those on the teton fault similar to 2 mm y 1 we compare the distribution of glacial erosion estimated from cirque floor elevations and last glacial maximum lgm equilibrium line altitude ela reconstructions and fault slip rate with three metrics of topography in each range the along strike maximum elevation swath profile hypsometry and slope elevation profiles in the slowly uplifting beaverhead bitterroot mountains and lemhi and lost river ranges trends in maximum elevation parallel elas independent of variations in fault slip rate maximum elevations are offset similar to 500 m from lgm elas in the lost river range lemhi range and northern beaverhead bitterroot mountains and by similar to 350 m in the southern beaverhead bitterroot mountains where glacial extents were less the offset between maximum topography and mean quaternary elas inferred from cirque floor elevations is similar to 350 m in the lost river and lemhi ranges and 200 250 m in the beaverhead bitterroot mountains additionally slope elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ela in the lemhi range and beaverhead bitterroot mountains suggesting that small glaciers efficiently limit topography the situation in the lost river range is less clear as a glacial signature is not apparent in either slope elevation profiles or the hypsometry in the rapidly uplifting teton range the distribution of elas appears superficially to correspond to maximum topography hypsometry and slope elevations profiles with regression lines on maximum elevations offset by similar to 700 and similar to 350 m from the lgm and mean quaternary ela respectively however grand teton and mt moran represent high elevation teflon peaks that appear impervious to glacial erosion formed in the hard crystalline bedrock at the core of the range glacier size and drainage density rock uplift rate and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography in the northern basin and range it is only under exceptional circumstances in the teton range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis c 2008 elsevier b v all rights reserved

numerical modeling of glacial erosion and headwall processes in alpine valleys abstract how rock relief is developed by glacial erosion in alpine landscapes is a key question in understanding the controls on mountain range topography any generation of relief by glaciers at the highest elevations in mountain ranges can affect the distribution of precipitation in alpine landscapes creating feedbacks between glacier mass balance and glacial erosion relief production at high elevation mountain crests is addressed using a numerical model that incorporates glacier dynamics and subglacial erosion as well as relevant hillslope processes blowing snow from a valley bounding plateau and avalanching onto the accumulation zone of the glacier is included in the model furthermore temperature dependent frost cracking is used as a proxy for headwall backwearing the parameterization of subglacial erosion produces about 500 m of erosion over the 400 ka of each numerical simulation in steady and varying climate scenarios valley floors flatten as headwalls increase in height and retreat headward over time headwall slopes increase in simulations in which quarrying is explicitly incorporated rates of quarrying are high near the base of the headwall increasing headwall length and slope as a result of valley floor lowering high rates of subglacial erosion and production of headwall relief also result when elastic flexural uplift occurs in response to mass unloading small overdeepenings form at the base of the headwall in steady climate simulations when the glacier is small at the end of the model run while the final profiles are relatively insensitive to the erosion rule used quarrying is most effective near the head of the glacier whereas rates of abrasion reflect the instantaneous pattern of integrated ice discharge or ice flux in simulations in which cirques are formed the equilibrium line altitude is hundreds of meters above the cirque floor however the time averaged horizontal position of the equilibrium line corresponds well with the downvalley position of the cirques

sedimentation pattern and tectonic evolution of the proterozoic singhbhum basin in the eastern indian shield abstract the proterozoic singhbhum basin psb located on the flank of an archaean platform ca 3400 ma is a distinct lithotectonic unit of the singhbhum crustal province of the eastern indian shield the present contribution traces the evolution of this basin filled by volcanics dominated submarine supracrustals and sedimentary formations the proterozoic singhbhum basin has been identified to be a marginal basin evolved in a back arc setting an axial volcanic belt manifesting mor like basaltic eruptions divided the basin into two domains with parallel but distinct sedimentation patterns an asymmetry in sedimentation pattern and source polarity are documented in litho as semblages and ree distribution patterns of cover rocks in the basinal domain flanking the southern platform prevailing tectonics strongly controlled the mechanism of sedimentation which coupled with the volcanic history of the basin indicates its riftogenic character progressive lithospheric stretching successively produced picritic volcanics and mor type basalts along the axial zone of the basin being related to a stretching factor of 2 continental margin rifting ultimately resulted in an oceanic transition as supported also by available geophysical data the evolution of the proterozoic singhbhum basin in its broad perspective was controlled by subduction related processes

relationship between tectonics volcanism sedimentation and basin development late cenozoic central part of northern honshu japan abstract a pronounced interplay between tectonics volcanism and sedimentation can be established in the volcanic arc region of the central part of northern honshu during the early miocene to quaternary interval four stages are recognized with the type of volcanism and sedimentation varying according to the tectonic stress regime 1 1 rifting stage 22 15 ma ns trending half grabens were formed under an extensional stress regime related to the rifting of the sea of japan basins were rapidly filled by intermediate to felsic volcanic products which are often associated with subaerial fluvial and lacustrine sediments 2 2 back arc basin opening stage 15 13 ma with more advanced stagess of rifting subsidence from crustal stretching resulted in marked marine incursion and an overall transgressive succession developed during this stage the back arc side of northern honshu subsided rapidly to middle bathyal environments at the same time associated with the opening of the sea of japan large volumes of regionally extensive mafic lavas and associated hyaloclastites were erupted within submarine grabens in contrast in the present backbone ranges felsic volcanism occurred within bathyal to shallow marine environments igneous rock types in this stage display a bimodal mafic felsic chemistry 3 3 transitional stage 13 2 4 ma a thermal subsidence substage 13 8 ma an intermediate stress regime developed which included phases of both weak extension and compression consequently grabens along the sea of japan ceased to form later lithospheric cooling eventually led to thermal subsidence of the back arc region and hemipelagic sediments mantled the previously active mafic volcanic apron volcanism at this time was mainly restricted to a narrow zone along the present backbone ranges where felsic to intermediate volcanic products accumulated within shallow marine environments b incipient compressional substage 8 2 4 ma hemipelagic sedimentation continued on the back arc side of northern honshu along the present backbone ranges the intermediate stress regime continued with formation of many large caldera structures associated with subaerial felsic volcanism 4 4 shortening deformation stage 2 4 ma present the change of the absolute direction of motion of the pacific plate at the early to middle pliocene changed the regional stress regime of the volcanic arc from intermediate to compression movement of back arc thrusts along the sea of japan coast began 2 3 ma and led to uplift of the volcanic arc continued compression in the volcanic arc produced narrow uplifted zones with associated basins bounded by reverse faults these basins were filled rapidly by terrestrial sediments containing upward coarsening sequences under this highly compressional tectonic stress regime volcanism became intermediate mafic in composition with large stratovolcanoes becoming prominent

cosmogenic exposure age chronologies of pinedale and bull lake glaciations in greater yellowstone and the teton range usa abstract we have obtained 69 new cosmogenic 10be surface exposure ages from boulders on moraines deposited by glaciers of the greater yellowstone glacial system and teton range during the middle and late pleistocene these new data combined with 43 previously obtained 3he and 10be ages from deposits of the northern yellowstone outlet glacier establish a high resolution chronology for the yellowstone teton mountain glacier complexes boulders deposited at the southern limit of the penultimate ice advance of the yellowstone glacial system yield a mean age of 136 13 10be ka and oldest ages of 151 157 10be ka these ages support a correlation with the bull lake of west yellowstone with the type bull lake of the wind river range and with marine isotope stage mis 6 end moraines marking the maximum pinedale positions of outlet glaciers around the periphery of the yellowstone glacial system range in age from 18 8 0 9 to 16 5 1 4 10be ka and possibly as young as 14 6 0 7 10be ka suggesting differences in response times of the various ice cap source regions moreover all dated pinedale terminal moraines in the greater yellowstone glacial system post date the pinedale maximum in the wind river range by 4 6 kyr indicating a significant phase relationship between glacial maxima in these adjacent ranges boulders on the outermost set and an inner set of pinedale end moraines enclosing jenny lake on the eastern teton front yield mean ages of 14 6 0 7 and 13 5 1 1 10be ka respectively the outer jenny lake moraines are partially buried by outwash from ice on the yellowstone plateau hence their age indicates a major standstill of an expanded valley glacier in the teton range prior to the younger dryas followed closely by deglaciation of the yellowstone plateau these new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the rocky mountains during the pleistocene

modeling topographic and climatic control of east west asymmetry in sierra nevada glacier length during the last glacial maximum 1 glaciers draining westward from the sierra nevada divide california during the last glacial maximum lgm were 7 times longer than east draining glaciers we address the degree to which this difference may be attributed to the topographic asymmetry of the west tilted sierran block and the climate asymmetry resulting from orographic modification of pacific ocean storms we simulate kilometer scale glaciers within the 50 50 km kings canyon region of the southern sierra by employing a two dimensional numerical model that is driven by simple spatially variable climates and treats ice transport by deformation sliding and avalanching in numerical experiments we match simulated termini to lgm moraine positions to constrain the parameters of different climate scenarios the 38 km long lgm glacier in kings canyon was reproduced by a climate specified by an equilibrium line altitude ela of 3170 m a mass balance gradient of 0 01 m yr m and a maximum positive balance of 2 m yr this climate generates much shorter average 6 km long east draining glaciers that however overshoot the lgm moraines by 1 km roughly 97 of the e w difference in glacier lengths can therefore be attributed to topographic asymmetry alone a second experiment suggesting a 120 m higher ela of 3290 m east of the divide can explain the shorter east draining glaciers an experiment in which orographic precipitation is explicitly simulated and melt is prescribed using a positive degree day algorithm matches both kings canyon and the average east draining glacier length with an lgm climate that was 5 6 c cooler and 2 times wetter than the modern sierra nevada

climate and ice sheet mass balance at the last glacial maximum from the genesis version 2 global climate model abstract at the last glacial maximum lgm about 21 000 calendar years ago 21 ka bp the overall mass balance of the laurentide and eurasian ice sheets should have been close to zero since their rate of change of total ice volume was approximately zero at that time the surface mass balance should have been zero or positive to balance any iceberg iceshelf discharge and basal melting but could not have been strongly negative in principle this can be tested by global climate model cgm simulations with prescribed ice sheet extents and topography we describe results from a suite of 21 ka bp simulations using a new global climate model genesis version 2 0 a with ssts prescribed from climap 1981 and predicted by a mixed layer ocean model and with ice sheets prescribed from clih the ice 4g peltier 1994 and climap 1981 reconstructions in common with previous gcm simulations using mixed layer oceans substantial cooling over and around antarctica occurs due to normal gcm dynamics and polar sea ice feedback without recourse to changes in thermohaline circulation we find slightly enhanced cooling and cloudiness over low latitude land masses compared to over ocean especially over the andes which decreases the disagreement with land based data and suggests that tropical climap ssts may only be 1 2 c too warm the gcm used here is well suited for ice sheet mass balance studies because i the surface can be represented at a finer resolution than the atmospheric gcm ii an elevation correction accounts for spectral distortions of the atmospheric gcm topography iii a simple post processing correction for refreezing of meltwater is applied and iv the model s precipitation and mass balances for present day greenland and antarctica are realistic however for all reasonable combinations of ssts and ice sheet configurations the predicted annual surface mass balances of the lgm laurentide and eurasian ice sheets are implausibly negative possible reasons for this discrepancy are discussed including increased ice age aerosols higher climap like ice sheet profiles in the few thousand years preceding lgm and a surge of the southern laurentide just before lgm to fleetingly produce the ice 4g profile at 21 ka bp

glacial topographic interactions in the teton range wyoming 1 understanding interactions among tectonics topography climate and erosion is fundamental to studies of mountainous landscapes here we combine topographic analyses with modeled distributions of precipitation insolation and flexural isostasy to present a conceptual model of topographic evolution in the teton range wyoming and test whether efficient glacial relief production has contributed to summit elevations the conceptual model reveals a high degree of complexity inherent in even a relatively small glaciated mountain range back tilting has caused topographic asymmetry with the greatest relief characterizing eastern catchments in the center of the range two high summits grand teton and mount moran rise hundreds of meters above the surrounding landscape their elevations set by the threshold hillslope angle and the spacing between valleys hosting large erosionally efficient glaciers only basins 20 km2 held glaciers capable of eroding sufficiently rapidly to incise deeply and maintain shallow downvalley gradients on the eastern range flank glacial erosion here was promoted by 1 prevailing westerly winds transporting snow to high relief eastern basins leading to cross range precipitation asymmetry 2 the wind blown redistribution of snow from open western headwaters into sheltered eastern cirques with the associated erosion driven migration of the drainage divide increasing eastern accumulation areas and 3 tall steep hillslopes providing shading snow influx from avalanching and insulating debris cover from rockfalls to valley floor glaciers in comparison the topographic enhancement of glacial erosion was less pronounced in western and smaller eastern basins despite dramatic relief production insufficient rock mass is removed from the teton range to isostatically raise summit elevations

volcaniclastic resedimentation in distal fluvial basins induced by large volume explosive volcanism the ebisutoge fukuda tephra plio pleistocene boundary central japan the ebisutoge fukuda tephra plio pleistocene boundary central japan has a well recorded eruptive style history magnitude and resedimentation styles despite the absence of a correlative volcanic edifice this tephra was ejected by an extremely large magnitude and complex volcanic eruption producing more than 400 km 3 total volume of volcanic materials volcanic explosivity index 7 which extended more than 300 km away from the probable eruption centre remobilization of these ejecta occurred progressively after the completion of a series of eruptions resulting in thick resedimented volcaniclastic deposits in spatially separated fluvial basins more than 100 km from the source facies analysis of resedimented volcaniclastic deposits was carried out in distal fluvial basins the distal tephra 100 300 km from the source comprises two different lithofacies primary pyroclastic fall deposits and reworked volcaniclastic deposits the resedimented volcaniclastic succession shows five distinct sedimentary facies interpreted as debris flow deposits facies a hyperconcentrated flow deposits facies b channel fill deposits facies c floodplain deposits with abundant flood flow deposits facies d and floodplain deposits with rare flood deposits facies e resedimented volcaniclastic materials at distal locations originated from unconsolidated deposits of a climactic large ignimbrite forming eruption factors controlling inter and intrabasinal facies changes are 1 temporal change of introduced volcaniclastic materials into the basin 2 proximaldistal relationship and 3 distribution pattern of pyroclastic flow deposits relative to drainage basins thus studies of the ebisutoge fukuda tephra have led to a depositional model of volcaniclastic resedimentation in distal areas after extremely large magnitude eruptions an aspect of volcaniclastic deposits that has often been ignored or poorly understood

late glacial fluctuations of the laurentide ice sheet in the white mountains of maine and new hampshire u s a abstract prominent moraines deposited by the laurentide ice sheet in northern new england document readvances or stillstands of the ice margin during overall deglaciation however until now the paucity of direct chronologies over much of the region has precluded meaningful assessment of the mechanisms that drove these events or of the complex relationships between ice sheet dynamics and climate as a step towards addressing this problem we present a cosmogenic 10be surface exposure chronology from the androscoggin moraine complex located in the white mountains of western maine and northern new hampshire as well as four recalculated ages from the nearby littleton bethlehem moraine seven internally consistent 10be ages from the androscoggin terminal moraines indicate that advance culminated 13 2 0 8 ka in close agreement with the mean age of the neighboring littleton bethlehem complex together these two datasets indicate stabilization or advance of the ice sheet margin in northern new england at 14 13 ka during the allerod greenland interstadial i

a shallow marine volcaniclastic facies model an example from sedimentary rocks bounding the subaqueously welded ordovician garth tuff north wales u k abstract volcaniclastic sedimentary rocks bounding the ordovician garth tuff in north wales were deposited in a shallow marine setting adjacent to a magmatic arc the volcaniclastic sedimentary rocks are primarily of angular to euhedral quartz angular euhedral feldspar and volcanic rock fragments these grains are of a pyroclastic origin but have been reworked to various degrees sedimentary rock fragments rounded quartz muscovite biotite iron rich chlorite and various clay minerals occur in lesser amounts the sedimentary rocks can be divided into a proximal offshore to foreshore facies association poffa and an offshore to lower shoreface facies association olsfa the sand dominated poffa exposed near capel curig is characterized by large wave ripples hummocky cross stratification co sets of trough cross beds reactivation surfaces plane beds and graded turbidite layers in suspension deposited mudstone water depths calculated from bedding plane exposure of large wave ripples and determined by the presence of hummocky cross stratification and by facies association vary from a few meters to around 30 m 45 50 m theoretical maximum in a 45 m thick stratigraphic section beneath the tuff eight kilometers to the southeast the garth tuff is bounded by a thick sequence of suspension deposited laminated mudstone with thin graded beds of siltstone and fine grained sandstone this facies association olsfa represents the introduction of material by distal turbidites and by pelagic sedimentation the olsfa was deposited in water depths well below storm wave base possibly in excess of 200 m no evidence of storm waves or surface generated currents occur until over 40 m above the tuff this study documents marine sedimentary rocks deposited in water depths ranging from foreshore to offshore as the bounding facies of the garth tuff it is thus reasonable to conclude that the garth tuff was emplaced and welded in water depths greater than the thickness of the tuff in the area of this study

latest pleistocene alpine glacier advances in the sawtooth mountains idaho usa reflections of midlatitude moisture transport at the close of the last glaciation mountain glaciers in the sawtooth mountains responded strongly to reinvigorated atmospheric moisture transport following the last ice sheet maximum the glaciers constructed an extensive moraine belt in the southeastern sawtooth mountains allowing determination of a detailed radiocarbon chronology from lake and marsh cores moraine morphometry and soil data indicate construction of seven to nine moraines in each of four valleys during two main late pleistocene ice advances a basal radiocarbon date from marsh cores in the alturas valley documents that the maximum advance during marine oxygen isotope stage 2 occurred shortly before ca 16 900 calibrated cal yr b p minimum limiting dates on glacial lacustrine sediment in lake and marsh cores from three valleys clustered around 13 950 cal yr b p document the maintenance or reestablishment of extensive ice volume during early late glacial time the ca 16 900 cal yr b p advance postdates the last ice sheet maximum by 4000 yr and is broadly correlative with maximum advances of the north yellowstone outlet glacier and the puget lobe of the cordilleran ice sheet and a near maximum advance of wallowa mountain glaciers these synchronous advances indicate response of a variety of ice systems to reinvigorated moisture transport following the ice sheet maximum as does the subsequent sawtooth advance during early late glacial time together these responses indicate strong sensitivity of certain ice systems to moisture delivery fluctuations

using ground penetrating radar and capacitively coupled resistivity to investigate 3 d fluvial architecture and grain size distribution of a gravel floodplain in northeast british columbia canada abstract this study combines ground penetrating radar gpr and capacitively coupled resistivity ccr for geophysical architecture analysis of a bar platform and channel bend on the floodplain of a poorly organized wandering gravel bed river an important objective of fluvial architectural analysis is linking fluvial style with preserved subsurface sedimentology however architectural analysis relies on opportunistic outcrops with locations or orientations that may not provide appropriate data gpr is a well established geophysical method that images reflections interpreted to represent bed geometry and bounding surfaces and is therefore ideal for imaging fluvial architecture unfortunately grain size information which is integral to architectural classification is more elusive using gpr resistivity data can be used as a proxy for sediment grain size when gpr and ccr are combined they offer an effective tool for geophysical fluvial architectural analysis five trenches provided direct observation of the subsurface sedimentology and are used to calibrate the two geophysical methods eight radar facies and one radar element are classified from the gpr survey and grouped into four categories horizontal and subhorizontal laterally continuous reflections group 1 clinoform reflections group 2 discontinuous reflections group 3 and concave up elements group 4 the 2 d resistivity data are combined in a gis to establish a 3 d resistivity model for the upper 5 m of the floodplain resistivity values correlate well with grain size and are categorized into fine grained 800 ohm m sediments in general resistivity values indicate coarse sediment in the bar platform and sand to fine grained material in the main channel and subordinate depressions resistivity profiles were extracted from the 3 d model along the gpr lines so that resistivity values could be directly compared to radar facies the shape and spread of the resistivity distributions provide dominant grain size as well as an indication of sediment sorting for individual radar facies in some cases the same radar facies is associated with markedly different grain sizes indicating different architectural elements i e horizontally bedded gravel verses horizontally bedded sand or fine grained sediment this demonstrates the utility of combining gpr and ccr insomuch as radar architecture alone is not diagnostic of fluvial architectural elements in this case study the bar platform and channel have a planform that might suggest a meandering fluvial style however gpr ccr results indicate that the dominant depositional process across the bar platform was vertical accretion of gravel sheets an architecture more consistent with a wandering gravel bed fluvial style lateral migration was limited to the outer downstream margin of the platform a location dominated by a mix of sand and gravel coarse gravel likely occupies the base of the main channel with fine grained sediment contributing to the remainder of the channel fill a four phase history is presented where the initial phase of development involves vertical accretion and migration of stacked gravel sheets during floods forming the core of the bar platform after flooding subsides and the interior bar emerges the channel becomes established and lateral migration becomes the dominant depositional process the evolution concludes with avulsion and eventual abandonment of the channel

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

amino acid paleothermometry of quaternary ostracodes from the bonneville basin utah abstract unlike many other proxy climate recorders temperature dependent chemical reactions that take place in fossils are independent of paleoprecipitation changes and therefore allow paleotemperatures to be calculated uniquely in this study i use the extent of amino acid racemization in fossil ostracode shells to reconstruct the temperature history of the bonneville basin utah the enantiomeric composition d l ratios of 64 ostracode samples each comprising an average of 18 subsamples from 25 sites were analyzed by reverse phase hplc the effective diagenetic temperature edt for five intervals of the quaternary including the last full glacial period was calculated for two amino acids aspartic and glutamic acids errors associated with the edt calculations were derived using a monte carlo procedure age control was provided by both new and previously published ams 14 c luminescence tephra and amino acid geochronology the edt for the southern bonneville basin during the middle pleistocene interval from 620 150 ka oxygen isotope stages ois 16 6 was 5 7 1 5 c this compares with an edt of 10 9 1 3 c for the late holocene last 5 8 cal ka and a current mean annual temperature of about 9 4 c at nearby sites 40 n latitude the edt then decreased to 3 3 1 3 c for the interval from ois 6 2 150 12 cal ka during the last full glacial period 24 12 cal ka ois 2 the edt was 1 1 2 5 c or about 10 3 c lower than during the late holocene paleotemperatures this low suggest that reduced evaporation rather than increased precipitation could have accounted for the increased effective moisture and the growth of lake bonneville

numerical reconstruction of a soft bedded laurentide ice sheet during the last glacial maximum we used a numerical ice sheet model to reconstruct the north american laurentide ice sheet during the last glacial maximum our model simulates ice sheet conditions that can be specified experimentally as either a rigid substrate hard bed or a wet deformable till soft bed basal sliding is excluded we use geologic records of former basal ice sheet processes to prescribe the distribution of hard and soft beds our reconstruction of the laurentide ice sheet is significantly lower in ice surface height and contains less ice volume than the climap maximum reconstruction in contrast our reconstruction agrees well with the ice 4g reconstruction both in height and volume because the ice 4g reconstruction is based on the inversion of relative sea level data whereas our reconstruction is based on glacial geology and ice mechanics this agreement suggests that soft beds provide a glaciological mechanism to explain the shape and volume of the laurentide ice sheet that is most consistent with observations of relative sea level change and other geodynamic considerations

modeled patterns of late pleistocene glacier inception and growth in the southern and central rocky mountains usa sensitivity to climate change and paleoclimatic implications abstract high resolution modern climate data for the southern and central rocky mountains provide a starting point for analysis of climate changes necessary to produce regional late pleistocene glaciation a gis based model was used to assess the sensitivity of glaciation in different ranges to climatic change and the combinations of temperature and precipitation change necessary to sustain the last glacial maximum lgm extent of glaciation in each range extensive glaciation initiates first in the wind river range of wyoming under every climate change scenario tested in absence of precipitation change a summer temperature depression of 6 8 c would be necessary to maintain lgm ice extents in colorado and wyoming if precipitation was halved necessary summer temperature depression would be 8 10 c if precipitation was doubled a depression of 3 5 5 5 c would suffice given model uncertainties these values may underestimate necessary temperature depression by as much as 2 c under all scenarios tested lgm glaciation in utah particularly the wasatch range requires either more temperature depression for given precipitation change or more precipitation for a given temperature depression than is required in the colorado wyoming rockies a summer temperature depression of 7 c which would suffice to sustain lgm ice extent with little change from modern precipitation in the colorado wyoming rockies would need to be coupled with a near doubling of precipitation to maintain lgm ice extent in the wasatch range this difference appears to reflect lgm precipitation enhancement in the wasatch range and to a lesser degree the uinta mountains resulting from the presence of lake bonneville immediately upwind of these ranges

cosmogenic 10be exposure dating of bull lake and pinedale moraine sequences in the upper arkansas river valley colorado rocky mountains usa

sedimentation history of the palaeoproterozoic dhanjori formation singhbhum eastern india abstract the palaeoproterozoic dhanjori formation eastern india is a terrestrial dominantly fluvial volcano sedimentary succession basal conglomerate coarse grained sandstone and shale rests directly on the granite basement and represents the distal fringe of an alluvial fan complex sieve sheet flood mass flow and alluvial channel and overbank deposits comprise the fan segment the rest of the formation is entirely constituted by fining upward fluvial cycles an event of basin tilting and volcanic eruption intervened and resulted a second phase of dhanjori sedimentation although the general fluvial depositional framework remained unaltered the two members of the dhanjori formation display different paleocurrent trends related to fluvial response to basin tilting in the lower member spatial variability in paleocurrent directions occurs as a consequence of fan development unlike the first phase the second phase of fluvial deposition incorporates profuse volcanics and accompanying volcaniclastic deposits these volcanic and volcaniclastic rocks might have locally blocked the river courses resulting in short lived lacustrine deposition composition of the volcanics varies upward from ultramafic to mafic the dhanjori volcanism took place in an intracontinental rift setting as is evident from the interbedded terrestrial deposits interbedded volcanic and volcaniclastic rocks in different stratigraphic levels suggest episodic volcanic eruption a semiarid paleoclimate is proposed and is consistent with development of an alluvial fan comprised of coarse clastic deposits

ice sheet inception subgrid hypsometric parameterization of mass balance in an ice sheet model studies of ice sheet inception and mountain glaciation are limited by model resolution in both atmospheric and glaciologic models the accumulation and ablation of snow and ice are controlled by local climate which is sensitive to topographic features that are subgrid in continent scale investigations climate patterns are complex in areas of high relief but the first order influence of elevation on temperature and atmospheric humidity is quantifiable and is central to glacier mass balance we make substantial improvements to the descriptions of accumulation and ablation in a large scale ice sheet model by incorporating subgrid topographic information the distribution of relief in the large scale model is estimated through a hypsometric parameterization based on the minimum maximum and median topographic elevation this permits accounting of high elevation accumulation and melting in deep valleys we combine this with a parameterization of downslope subgrid ice flux simulating but not explicitly describing the role of alpine glaciers the detailed budgeting of mass balance greatly improves our skill in modelling present day ice distribution in north america we anticipate similar improvements in our ability to model nucleation centres of the quaternary ice sheets this approach may also prove useful in projections of glacier and ice field response to climate change

climate at the equilibrium line of glaciers the relationships between temperature precipitation and radiation on glacier equilibrium lines are investigated using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods it is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months temperature in a free atmosphere annual total precipitation and the sum of global and long wave net radiation all of these are measured at or very near the equilibrium line altitudes then it is shown how the shift of the equilibriumline will occur as a result of a climatic change finally the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations the present results make it possible to identify the altitudes in climate models where glacierization should begin and to evaluate the mass balance changes as a result of possible future changes in the climate

valley asymmetry and glacial versus nonglacial erosion in the bitterroot range montana usa theories that propose feedbacks among climate tectonics and surface processes commonly assume that erosion is enhanced by glacial activity indeed studies have shown that glaciers appear to limit the elevation of mountain ranges however comparisons between rates of glacial and nonglacial erosion are difficult to make ideally such comparisons must hold precipitation and lithology constant while only varying the erosional regime located in a climatic transition zone during the pleistocene the east west trending valleys of the bitterroot range present an opportunity for a quantitative analysis of glacial and nonglacial erosion because the north facing sides of the valleys were glaciated whereas the south facing slopes were not the different erosional regimes operating on either side of the valleys created strongly asymmetric ridges ridgelines separating the east west trending valleys have been pushed southward by glacial headwall retreat such that ridge to valley distances are 50 greater on the north facing slopes than on the south facing slopes in addition mean hillslope angles are 6 lower on the glaciated slopes than on the unglaciated slopes and calculations of geophysical relief suggest that on average glaciers have removed nearly twice as much rock as nonglacial processes finally we conclude that although rates of vertical incision by glacial processes in the bitterroot range were more rapid than nonglacial processes the dominant geomorphological impact of glaciers was lateral erosion by headwall retreat

debris flow and hyperconcentrated flood flow deposits in an alluvial fan northwestern part of the cretaceous yongdong basin central korea abstract the alluvial fan deposits in the cretaceous yongdong basin korea consist of conglomerates with a muddy or sandy matrix and sandstones with thick or thin laminations the conglomerates and sandstones occur commonly in couplets constituting apparently single sedimentation units facies transitions in the deposits can be summed up in a tripartite facies sequence 1 a clast supported conglomerate with a muddy or sandy matrix and parallel clast alignment facies a and b 2 a matrix supported coarse tail normally graded conglomerate with random clast orientation facies c and thickly stratified pebbly sandstone facies d and 3 laminated sandstone facies e the clast supported conglomerate is interpreted as deposits of debris flows dominated by frictional grain interactions development of pervasive parallel clast alignment lacking large floating clasts and inverse grading suggests deposition via incremental aggradation rather than en masse freezing the matrix supported conglomerate an

chronology of glaciations in the sierra nevada california from 10be surface exposure dating abstract we use 10 be surface exposure dating to construct a high resolution chronology of glacial fluctuations in the sierra nevada california most previous studies focused on individual glaciated valleys whereas our study compares chronologies developed throughout the range to identify regional patterns in the timing of glacier response to major climate changes sites throughout the range indicate last glacial maximum retreat at 18 8 1 9 ka 2 that suggests rather consistent changes in atmospheric variables e g temperature and precipitation throughout the range the penultimate glacial retreat occurred at ca 145 ka our data suggest that the sierra nevada landscape is dominated by glacial features deposited during marine isotope stage mis 2 and mis 6 deposits of previously recognized glaciations between circa 25 and 140 ka e g mis 4 tenaya early tahoe cannot be unequivocally identified the timing of sierra nevada glacial retreat correlates well with other regional paleoclimate proxies in the sierra nevada but differs significantly from paleoclimate proxies in other regions our dating results indicate that the onset of lgm retreat occurred several thousand years earlier in the sierra nevada than some glacial records in the western us

tidal sandwaves and related storm deposits in the transgressive protoproterozoic chaibasa formation india abstract despite deformation and metamorphism the 2 3 ga fine grained siliciclastic chaibasa formation of eastern india locally retains an excellent record of sandwave migration under the influence of tides and storms within a precursor sandstone facies in a largely subtidal setting and provides a rare opportunity to detect tidal periodicities in the finer facies locally preserved minor features provide glimpses of the depositional mechanisms and settings the silt dominated precursor heterolithic silt mud facies contain numerous slides and slumps and was formed on a relatively steep slope between the fairweather and storm wave bases the shale facies formed in a deeper setting beneath the wave base earthquakes occasionally have interrupted normal sedimentation and massflow products are present in all the facies but with increasing frequency within the finer facies the sandstone facies units which were emplaced during repeated lowstands were first subjected to progradation and subsequently drowned in an overall transgression trend

updated cosmogenic chronologies of pleistocene mountain glaciation in the western united states and associated paleoclimate inferences abstract surface exposure dating with terrestrial cosmogenic nuclides tcns has become the primary method for determining numerical ages of pleistocene mountain glacial deposits and landforms in the conterminous western united states u s and in numerous other glaciated settings worldwide recent updates to models of tcn production and scaling warrant a reconsideration of published exposure ages of moraines of the last two pleistocene glaciations and associated paleoclimate inferences previously reported tcn exposure ages of moraines are recalculated here using newer production rates and scaling models for nuclides helium 3 3he beryllium 10 10be aluminum 26 26al and chlorine 36 36cl in most cases yielding significant differences from originally reported ages recalculated tcn exposure ages of moraines of the penultimate glaciation display a high degree of variability for individual landforms particularly toward the younger end of age distributions suggesting that exposure history is affected by moraine denudation and that older age modes provide the best estimate of the depositional age of these moraines oldest exposure ages of penultimate glaciation moraines are well aligned among mountain ranges across the western u s and yield a mean of 138 13 ka indicating that mountain glaciation occurred in step with global ice volume maxima during marine oxygen isotope stage 6 on average terminal moraines of the last glaciation date to 19 5 2 3 ka and correspond to the latter part of the global last glacial maximum lgm down valley recessional moraines representing prolonged glacial stabilizations or readvances to 75 of maximum lengths have a mean exposure age of 17 0 1 8 ka suggesting that these moraine positions were last occupied during heinrich stadial 1 evidence for multiple glacial culminations during the last glaciation is found in several mountain ranges and likely reflects at least two phases of late pleistocene climate an earlier phase when glaciers attained their maximum length in response to cooling during the lgm and a later phase when glaciers persisted at or readvanced to near maximum lengths in response to sustained cold temperatures and or increased precipitation

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

timing and patterns of debris flow deposition on shepherd and symmes creek fans owens valley california deduced from cosmogenic 10be debris flow fans on the western side of owens valley california show differences in their depths of fan head incision and thus preserve significantly different surface records of sedimentation over glacial interglacial cycles we mapped fan lobes on two fans symmes and shepherd creek based on the geometry of the deposits using field observations and high resolution airborne laser swath mapping alsm data and established an absolute fan lobe chronology by using cosmogenic radionuclide exposure dating of large debris flow boulders while both fans and their associated catchments were subject to similar tectonic and base level conditions the shepherd creek catchment was significantly glaciated while that of symmes creek experienced only minor glaciation differences in the depth of fan head incision have led to cosmogenic surface age chronologies that differ in the length of the preserved depositional records symmes creek fan preserves evidence of exclusively holocene deposition with cosmogenic 10be ages ranging from 8 to 3 ka in contrast the shepherd creek fan surface was formed by late pleistocene and holocene debris flow activity with major deposition between 86 74 33 15 and 11 3 ka these age constraints on the depositional timing in owens valley show that debris flow deposition in owens valley occurred during both glacial and interglacial periods but may have been enhanced during marine isotope stages 4 and 2 the striking differences in the surface record of debris flow deposition on adjacent fans have implications for the use of fan surfaces as paleoenvironmental recorders and for the preservation of debris flow deposits in the stratigraphic record

latest pleistocene advance of alpine glaciers in the southwestern uinta mountains utah usa evidence for the influence of local moisture sources cosmogenic surface exposure 10 be dating of last glacial maximum lgm moraines indicates that glaciers in the southwestern uinta mountains remained at their maximum positions until ca 16 8 0 7 ka 2 k y after glaciers in the neighboring wind river range and colorado rockies began to retreat the timing of the local lgm in the south western uintas overlaps with both the hydrologic maximum of lake bonneville and pre liminary estimates of the local lgm in the western wasatch mountains this broad syn chroneity indicates that lake bonneville and glaciers in northern utah were responding to similar climate forcing furthermore equilibrium line altitudes elas for reconstruct ed lgm alpine glaciers increase with distance from the lake bonneville shoreline rising from 2600 m to 3200 m over the 120 km length of the glaciated uintas this pro nounced ela gradient suggests that the magnitude of the latest pleistocene glacial advance in the western uintas was due at least in part to enhanced precipitation derived from lake bonneville thus the lake acted as a local amplifier of regional climate forcing this relationship underscores the sensitivity of alpine glaciers to moisture availability during the latest pleistocene and further demonstrates the importance of local moisture sources on glacier mass balance

architectural elements and bounding surfaces in fluvial deposits anatomy of the kayenta formation lower jurassic southwest colorado abstract three well exposed outcrops in the kayenta formation lower jurassic near dove creek in southwestern colorado were studied using lateral profiles in order to test recent regarding architectural element analysis and the classification and interpretation of internal bounding surfaces examination of bounding surfaces within and between elements in the kayenta outcrops raises problems in applying the three fold classification of allen 1983 enlarging this classification to a six fold hierarchy permits the discrimination of surfaces intermediate between allen s second and third order types corresponding to the upper bounding surfaces of macroforms and internal erosional reactivation surfaces within the macroforms examples of the first five types of surface occur in the kayenta outcrops at dove creek the new classifications is offered as a general solution to the problem of description of complex three dimensional fluvial sandstone bodies the kayenta formation at dove creek consists of a multistorey sandstone body including the deposits of lateral and downstream accreted macroforms the storeys show no internal cyclicity neither within individual elements nor through the overall vertical thickness of the formation low paleocurrent variance indicates low sinuosity flow whereas macroform geometry and orientation suggest low to moderate sinuosity the many internal minor erosion surfaces draped with mud and followed by intraclast breccias imply frequent rapid stage fluctuation consistent with variable seasonal monsonal ephemmeral flow the results suggest a fluvial architecture similar to that of the south saskatchewan river through with a three dimensional geometry unlike that interpreted from surface studies of that river

late pleistocene climate inferred from the reconstruction of the taylor river glacier complex southern sawatch range colorado abstract ice surface topography of a late pleistocene glacier complex herein named the taylor river glacier complex trgc was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps during the last glacial maximum lgm the trgc covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and or upland ice fields equilibrium line altitudes elas for the glaciers of the trgc were estimated using the accumulation area ratio method assuming that ratio to be 0 65 0 05 elas thus derived ranged from about 3275 to 3400 m with a mean of 3340 60 m a degree day model ddm was used to infer the climatic significance of the lgm ela with no appreciable differences in precipitation with respect to modern climate the ela implies that mean summer temperatures during the lgm were 7 6 c cooler than today the ddm was also used to determine the temperatures required to maintain steady state mass balances for each of the reconstructed glaciers the required reductions in summer temperature vary little about a mean of 7 1 c the sensitivity of these results to slight 25 changes assumed for lgm precipitation are less than 0 5 c even under an lgm climate in which precipitation is assumed to be substantially different 50 than the present mean summer temperatures must be on the order of 7 0 to 8 5 c lower to depress equilibrium lines to lgm altitudes the greater sensitivity of the ela to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation

the electric moho underneath eastern indian craton 1 moho boundary discovered about a century back is well established on the basis of seismological studies electromagnetic studies using very low frequencies however have not been able to establish this boundary due to the presence of highly conducting continental lower crust magnetotelluric lithospheric study over the eastern indian craton 3 3 gyr resolves the lower crust and upper mantle boundary due to the absence of highly conducting continental lower crust underneath the craton from the present study it can be speculated that a dynamics other than the plate tectonics possibly existed up to the mid archaean

the influence of continental ice sheets on the climate of an ice age the climate influence of the land ice that existed 18 000 years before present 18k b p is investigated by use of a general circulation model of the atmosphere coupled with a static mixed layer ocean simulated climates are obtained from two versions of the model one with the land ice distribution of the present and the other with that of 18k b p in the northern hemisphere the tropospheric flow field is strongly influenced by the laurentide ice sheet and features a split flow straddling the ice sheet with a strong jet stream forming the southern branch the northern branch of the flow brings very cold air over the north atlantic ocean where thick sea ice is maintained the distribution of sea surface temperature sst difference between the two experiments in the northern hemisphere resembles the difference between the sst at 18k b p and at present as estimated by the climap project 1981 the 18k b p ice sheets have very little influence upon atmospheric temperature and sst in the southern hemisphere this is because the interhemispheric heat transport hardly changes as the loss of heat energy due to the reflection of solar radiation by continental ice sheets in the northern hemisphere is almost completely counterbalanced by the in situ reduction of upward terrestrial radiation hydrologic changes in the model climate are also found with statistically significant decreases in soil moisture occurring in a zone located to the south of the ice sheets in north america and eurasia these findings are consistent with some geological evidence of regionally drier climates from the last glacial maximum

variable responses of western u s glaciers during the last deglaciation cosmogenic 10 be exposure ages from moraines in the wallowa mountains oregon identify two maximal late pleistocene glaciations at 21 1 6 0 4 ka and 17 0 6 0 3 ka and a minor glacial event at 10 2 6 0 6 ka our new high resolution chronology integrated with other well dated glacial records from the western united states demonstrates sub stantial differences in the synoptic responses of western u s glaciers to climate forcing associated with the global last glacial maximum and subsequent millennial scale events originating in the north atlantic region these variable synoptic glacier responses identify large changes in the relative contributions of regional to global controls on the climate of the western united states that accompanied the deglaciation