litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

the internal sediment architecture of a drumlin port byron new york state usa abstract an exposure within the central portion of a large drumlin at port byron new york state usa part of the large new york drumlin field reveals a sequence of steeply dipping cemented sands and gravels of proglacial ice contact deltaic origin overlain by a thin till veneer the sands and gravels appear to have been deposited within the proximal proglacial environment during a late retreat phase of the laurentide ice sheet sometime prior to being overridden by subsequent ice and drumlinized during deposition of the ice contact delta escaping subglacial regelation meltwater permeated the proximal deltaic sediment pile and calcium carbonate was released in a series of pulses to form pore occluding calcite cement within the sand and gravel porespaces the calcium carbonate precipitated into the sands and gravels due to a reduction in hydrostatic pressure and co2 outgassing of the meltwater as it exited from beneath the ice sheet once cemented these deltaic sediments were considerably stronger and acted afterward as an obstacle around which the future ice advance streamed and in turn produced the characteristic drumlin shape in overriding the ice contact deltaic sediments the ice sheet emplaced a thin layer of till which exhibits syndepositional deformation features indicative of being emplaced as a deforming bed layer beneath the advancing ice sheet micromorphological analysis of the overlying till shows that no interstitial or intraclastic calcite occurs within the till

deep mantle forces and the uplift of the colorado plateau 1 we introduce a quantitative model of global mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 ma towards the interior of the southwestern usa from observed present day mantle heterogeneity the onset and evolution of uplift in the central basin and range province and colorado plateau during this time is determined by tracking the topographic swell due to this mantle upwelling we show that 1 the extension and basaltic volcanism post 25 ma in the central basin and range coincides with the arrival and eastward progression of this upwelling and 2 dynamic uplift of the southern colorado plateau totaling about 1 km transpired in the last 20 ma since 10 ma the center of uplift continued northeastward from the southwestern rim of the plateau consistent with a young grand canyon model and eastward sweep of magmatism in the western colorado plateau

the subglacial thermal organisation sto of ice sheets abstract this paper examines ice sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid latitude ice sheets the laurentide cordilleran fennoscandian and british irish ice sheets we compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary antarctic ice sheet inferred from radarsat 1 antarctic mapping project ramp data the evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice dynamical components that collectively define the subglacial thermal organisation sto of ice sheets these ice dynamical components are frozen bed patches ice streams ice stream tributaries and lateral shear zones frozen bed patches appear at a wide range of spatial scales spanning four orders of magnitude in some areas frozen bed zones comprise large proportions of the bed e g near the ice divide in continental areas whilst in other areas they constitute isolated islands in areas dominated by thawed bed conditions ice streams narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow are also common features of quaternary ice sheets tributaries to ice streams flow at velocities intermediate between full ice stream and sheet flow and may divert ice drainage from one primary ice stream corridor to an adjacent one sharp lateral boundaries between landforms indicate sliding and non sliding conditions respectively these lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed bed ice streams and intervening frozen bed areas we use the landform evidence in the area around great bear lake canada to trace the evolution of an ice stream web through time demonstrating that frozen bed patches are integral components of this complex system we conclude that frozen bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams

eemian and early weichselian environments in southern sweden a multi proxy study of till covered organic deposits from the smaland peneplain based on their luminescence and infinite radiocarbon ages organic deposits beneath till at two sites on the smaland peneplain southern sweden nybygget and stora gaddevik are concluded to have formed before the middle weichselian applied palaeoecological methods include analyses of pollen diatoms charcoal fragments macroscopic remains of vascular plants and mosses and insect remains pollen stratigraphical correlations with previously studied interglacial interstadial sites in southern sweden denmark and northern germany suggest that the peat at nybygget dates from the brorup interstadial or the final stage of the eemian interglacial whereas the lake sediments at stora gaddevik probably were emplaced during the middle eemian we conclude that the peat was formed in a wetland characterized by both wood swamp and open mire vegetation and surrounded by semi open woodlands dominated by pine birch and hazel the middle eemian sequence at the stora gaddevik site provides evidence of a moderately nutrient rich to nutrient rich lake environment with relatively diverse aquatic vegetation regional vegetation as reconstructed using the reveals model was spruce woodland mixed with pine alder and birch but also included more open environments with hazel oak grasslands and sedge dominated wetlands water shield brasenia schreberi now extinct in europe was identified in the eemian lake deposits from both pollen and macroscopic remains

the last interglacial glacial cycle in ne fennoscandia a nearly continuous record from sokli finnish lapland abstract boreholes from the sokli basin in finnish lapland have recovered a unique sequence of diamicts interlayered with fine grained sediments that are rich in fossils the diamicts are interpreted as till beds deposited by the fennoscandian ice sheet the fine grained intercalations seem to represent a series of warm stages that include one interglacial and three interstadials the interglacial is characterized by a mixed taiga pollen assemblage and corresponds to a distinct diatom gyttja bed the interstadials show progressively colder floras from open birch forest to arctic forest limit to shrub tundra their sediments comprise gyttja interlayered with wood and sand interstadial 1 sands grading into sandy gyttja interstadial 2 and sands overlain by laminated silt and clay interstadial 3 the interstadial 2 and 3 deposits are underlain by diamict and are interpreted as deglaciation sequences silts with a tundra pollen assemblage separate the interglacial and interstadial 1 deposits luminescence dating evidence indicates that the interglacial bed most probably represents the nw european mainland eemian interglacial marine isotope stage mis 5e the interstadial 1 2 and 3 deposits are tentatively correlated with the early weichselian brorup and odderade interstadials and an interstadial of middle weichselian age respectively mis 5c 5a and 3 respectively the correlation implies that the easternmost part of the ice divide zone of the fennoscandian continental ice sheet was deglaciated during part of mis 3

present day temperatures in northern scandinavia during the last glaciation scandinavia is generally considered to have been covered extensively with ice throughout marine isotope stages mis 4 2 between 75 and 10 ka here we present evidence for ice free warm conditions in the central area of the scandinavian glaciations during mis 3 our multiproxy data obtained from a lacustrine sequence in northern fin land reveal not only significant response in the northeastern sector of the scandinavian ice sheet to warming during the early part of mis 3 but also indicate rapid climate warming to present day temperatures in this ice free period new climate model simulations for interstadial conditions in mis 3 confirm the high mean july temperatures northeast of the scandinavian ice sheet in response to the high insolation values and the presence of the ice sheet during mis 3

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

simultaneous inversion of mantle properties and initial conditions using an adjoint of mantle convection through the assimilation of present day mantle seismic structure adjoint methods can be used to constrain the structure of the mantle at earlier times i e mantle initial conditions however the application to geophysical problems is restricted through both the high computational expense from repeated iteration between forward and adjoint models and the need to know mantle properties such as viscosity and the absolute magnitude of temperature or density a priori we propose that an optimal first guess to the initial condition can be obtained through a simple backward integration sbi of the governing equations thus lessening the computational expense given a model with known mantle properties we show that a solution based on an sbi generated first guess has smaller residuals than arbitrary guesses mantle viscosity and the effective rayleigh number are crucial for mantle convection models neither of which is exactly known we place additional constraints on these basic mantle properties when the convection induced dynamic topography on earth s surface is considered within an adjoint inverse method besides assimilating present day seismic structure as a constraint we use dynamic topography and its rate of change in an inverse method that allows simultaneous inversion of the absolute upper and lower mantle viscosities scaling between seismic velocity and thermal anomalies and initial condition the theory is derived from the governing equations of mantle convection and validated by synthetic experiments for both one layer viscosity and two layer viscosity regionally bounded spherical shells for the one layer model at any instant of time the magnitude of dynamic topography is controlled by the temperature scaling while the rate of change of topography is controlled by the absolute value of viscosity for the two layer case the rate of change of topography constrains upper mantle viscosity while the magnitude of dynamic topography determines the temperature scaling lower mantle viscosity when upper mantle lower mantle density anomaly dominates the flow field this two stage scheme minimizes the tradeoff between temperature and lower mantle viscosity for both cases we show that the theory can constrain mantle properties with errors arising through the adjoint recovery of the initial condition for the two layer model this error is manifest as a tradeoff between the temperature scaling and lower mantle viscosity

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

seismically imaged relict slab from the 55 ma siletzia accretion to the northwest united states teleseismic tomography images a large high velocity curtain extending vertically beneath the ca 50 ma challis magmatic trend to maximum depths of 230 600 km we interpret this structure as subducted farallon ocean lithosphere that stalled with the ca 55 ma accretion of the siletzia microplate to north america within the columbia embayment and we consider the regional tectonic implications the abrupt switch ca 53 ma from laramide thrusting and magmatic quiescence to extension and vigorous magmatism in the northwestern united states is evidence for foundering of the fl at subducting farallon slab to account for the imaged curtain foundering apparently occurred by rollback after siletzia accretion terminated subduction within the columbia embayment the magnitude of the high seismic velocity curtain is approximately that expected for 20 50 m y old ocean lithosphere that stalled in the upper mantle ca 50 ma we suggest that the stalled slab became nearly neutrally buoyant as a result of removal of its basaltic crust the melting of which likely contributed to the short lived vigor of challis magmatism after siletzia accretion normal dip cascadia subduction initiated west of siletzia evidenced by arc volcanism in oregon and washington beginning ca 45 40 ma while continued quiescence of the sierra nevada arc suggests persistence of flsubduction to the south kinematically this requires a tear in the subducted farallon slab near the latitude of southern oregon we propose that north to south propagation of this torn slab edge propagated the ignimbrite fl are up across what now is the northern basin and range and ended the laramide orogeny

influence of climate change and uplift on colorado plateau paleotemperatures from carbonate clumped isotope thermometry the elevation history of earth s surface is key to understanding the geodynamic processes responsible for the rise of plateaus we investigate the timing of colorado plateau uplift by estimating depositional temperatures of tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry a measure of the temperature dependent enrichment of 13 c 18 o bonds in carbonates comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern united states reveals a lake water carbonate temperature lct lapse rate of 4 2 0 6 c km analysis of miocene deposits from 88 to 1900 m elevation in the colorado river drainage suggests that the ancient lct lapse rate was 4 1 0 7 c km and temperatures were 7 7 2 0 c warmer at any one elevation than predicted by the modern trend the inferred cooling is plausible in light of pliocene temperature estimates off the coast of california and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 ma together with previous paleorelief estimates from apatite u th he data from the grand canyon our results suggest most or all of the plateau s lithospheric buoyancy was acquired 80 60 ma and do not support explanations that ascribe most plateau uplift to oligocene or younger disposal of either the farallon or north american mantle lithosphere

early mis 3 glacial lake evolution ice marginal retreat pattern and climate at sokli northeastern fennoscandia lake development at sokli northern finland is traced through the analysis of diatoms and other siliceous micro fossils in a 2 meter thick minerogenic laminated clay silt deposit dated to the early part of marine isotope stage mis 3 fluctuating water levels and changes in lake extent depicted by the siliceous micro fossil record together with lithology suggest that an important part of the sediment sequence was deposited in a glacial lake the proxy based glacial lake evolution is tested using a digital elevation model and geomorphologic evidence including eskers dated to the early mis 3 tulppio interstadial at sokli despite the apparent ice dammed nature of the lake the sediment is relatively rich in fossils and there are limited signs of re deposition of older fossil material the siliceous micro fossil record together with data from other proxies previously analysed in the same sediment samples provides a coherent picture of past environmental changes around the sokli site this is most probably due to the sheltered position of the coring site in a lake embayment quantitative climate reconstructions based on the diatom record show mean july air temperatures as high as present day values at sokli and the temperature ranges indicated by the diatom record are in agreement with temperature reconstructions based on chironomids the position of sokli in the northeastern portion of the central area of the scandinavian glaciations and the northern retreat pattern implies that an important part of eastern fennoscandia was deglaciated during the early mis 3 warming event

mantle circulation models with variational data assimilation inferring past mantle flow and structure from plate motion histories and seismic tomography summary mantle convection models require an initial condition some time in the past because this initial condition is unknown for earth we cannot infer the geological evolution of mantle flow from forward mantle convection calculations even for the most recent mesozoic and cenozoic geological history of our planet here we introduce a fluid dynamic inverse problem to constrain unknown mantle flow back in time from seismic tomographic observations of the mantle and reconstructions of past plate motions using variational data assimilation we derive the generalized inverse of mantle convection and explore the initial condition problem in high resolution 3 d spherical mantle circulation models for a time period of 100 myr roughly comparable to half a mantle overturn we present a synthetic modelling experiment to demonstrate that mid cretaceous mantle structure can be inferred accurately from fluid dynamic inverse modelling assuming present day mantle structure is well known even if an initial first guess assumption about the mid cretaceous mantle involved only a simple 1 d radial temperature profile we also demonstrate that convecting present day mantle structure back in time by reversing the time stepping of the energy equation is insufficient to model the mantle structure of the past the difficulty arises because such backward convection calculations ignore thermal diffusion effects and therefore cannot account for the generation of thermal buoyancy in boundary layers as we go back in time inverse mantle convection modelling should make it possible to infer a number of flow parameters from observational constraints of the mantle

density and lithospheric strength models of the yellowstone snake river plain volcanic system from gravity and heat flow data abstract the structure and composition of the yellowstone snake river plain ysrp volcanic system were analyzed using gravity data taken at over 30 000 stations in the ysrp and surrounding region additional constraints were provided by tomographic seismic velocity models new heat flow and temperature information gps derived strain rates earthquake locations and chemical analyses of volcanic rocks p wave velocity models and velocity density data based on petrologic information were used to constrain three dimensional density models rheology and strength properties were calculated at selected locations and compared to earthquake focal depths results of this study suggest that the lower crust of the snake river plain srp has been thickened by the addition of an underplated layer composed primarily of clinopyroxene having a density of 3200 kg m3 a mid crustal high density sill is composed of a series of gabbroic lenses inter fingering with the granitic upper crust this geometry yields a bulk composition comparable to diorite and a density of 2900 kg m3 the mid crustal sill varies from 4 to 11 km in thickness resulting in a series of se nw trending gravity highs observed along the axis of the srp the mid crustal sill extends up to 20 km southeast of the srp volcanic field and causes asymmetry of the gravity field the yellowstone plateau volcanic field density model reveals low density partial melt 10 km beneath the caldera that shallows under the northeastern caldera and continues laterally 20 km north of the caldera boundary and notably increases the previously estimated size of the magma reservoir by 20 the caldera melt body has a density of 2520 kg m3 and a significantly lower value of 2470 kg m3 for the northeastern caldera melt body southwest of yellowstone the crustal section occupied by the mid crustal sill in the srp and the partial melt in yellowstone constitute a transition area between the active yellowstone magma system and the now volcanically quiescent srp with a density of 2820 kg m3 strength models show that the crust of the ysrp becomes progressively stronger and cooler with increasing distance from yellowstone and tectonic earthquakes within the yellowstone caldera are unlikely to nucleate below 4 6 km depth thus limiting the maximum magnitude of earthquakes to m 6 5

dynamic topography gravity and the role of lateral viscosity variations from inversion of global mantle flow lateral viscosity variations lvvs in the mantle influence geodynamic processes and their surface expressions with the observed long wavelength geoid free air anomaly gravity gradient in three directions and discrete high accuracy residual topography we invert for depth and temperature dependent and tectonically regionalized mantle viscosity with a mantle flow model the inversions suggest that long wavelength gravitational and topographic signals are mainly controlled by the radial viscosity profile the pre cambrian lithosphere viscosity is slightly one order of magnitude higher than that of oceanic and phanerozoic lithosphere plate margins are substantially weaker than plate interiors and viscosity has only a weak apparent dependence on temperature suggesting either a balancing between factors or a smoothing of actual higher amplitude but short wavelength lvvs the predicted large scale lithospheric stress regime compression or extension is consistent with the world stress map thrust or normal faulting both recent compiled high accuracy residual topography and the predicted dynamic topography yield 1 km amplitude long wavelength dynamic topography inconsistent with recent studies suggesting amplitudes of 100 to 500 m such studies use a constant positive admittance transfer function between topography and gravity in contrast to the evidence which shows that the earth has a spatially and wavelength dependent admittance with large negative admittances between 4000 and 10 4 km wavelengths

mass transfer along the yellowstone hotspot track ii kinematic constraints on the volume of mantle derived magma abstract this paper evaluates the neogene kinematic evolution of the eastern snake river plain esrp to estimate the volume of mafic magma transferred from mantle to crust during passage over the yellowstone hotspot four major kinematic processes affected the esrp including densification due to emplacement of gabbro into the middle crust subsidence and consequent filling of a 6 km deep basin with volcanic and plutonic rocks 20 extension via dike injection or faulting ductile attenuation and lower crustal flow from esrp to the adjacent basin and range two kinematic models involving these processes are proposed overall the two models are viable only if the initial crustal thickness were 43 47 km thick otherwise the lost mass of the esrp is not balanced by the excess mass in the basin and range in the first model densification eruption and extension by dike injection the esrp crust receives mantle derived gabbro equivalent to a 16 km thick layer but would need to lose 10 km of crust via lower crustal flow in the second model densification eruption and extension by faulting and ductile attenuation the esrp crust receives a 9 4 km equivalent thickness of mantle derived gabbro and would need to lose 6 km of crust via lower crustal flow the cumulative amount of mantle derived gabbro in the esrp crust derived by this kinematic analysis equivalent to a 9 4 16 km thick layer is nearly identical to the amount estimated independently using a mass balance petrologic model suggesting it is a robust result

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

global dynamic topography observations reveal limited influence of large scale mantle flow mantle flow causes earth s surface to uplift and subside global analysis of dynamically generated topography suggests that temperature induced small scale mantle flow has a bigger influence on surface topography than large scale mantle flow

quaternary glaciations of northern europe this paper presents the outcome of a workshop held in berlin in february 2009 concerned with current research on the glacial history of northern europe including the british isles the methodologies presently used to resolve this topic are outlined particular attention is given to new analytical methods deriving from high resolution remote imaging of glacial terrain both on land and on the sea bed key new stratigraphic sections higher resolution results from conventional geochronological methods like radiocarbon and more recently developed technologies such as luminescence and cosmogenic radionuclide dating the relationships between the results derived from these two methods are discussed in further detail along with possible explanations for these differences an outline of a most likely glacial history of the scandinavian and british and irish ice sheets is presented along with possible links to global climate change as represented by the marine isotope mis record tentative evidence for glaciation is identified in mis 22 16 12 10 8 6 4 and 2 and correlations of phases within the last glaciation are also explored for both the scandinavian and british and irish ice sheets the results show that the character and extent of glaciation in different parts of the region are not synchronous and much more geochronological work is required before regional correlations can be established with confidence

a middle weichselian interstadial lake deposit on sejero denmark macrofossil studies and dating studies of lake sediments on sejero in southern kattegat indicate a treeless arctic environment with the dwarf shrub salix polaris herbs and wetland mosses the mean july temperature was around 8 to 10 c an ams radiocarbon age determination of a salix twig yielded an age of around 36 000 14c yr bp which is in accordance with previous conventional dating of bulk sediment samples copyright 2006 john wiley sons ltd

an arctic perspective on dating mid late pleistocene environmental history to better understand pleistocene climatic changes in the arctic integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required not least for correlation to extra arctic records in this paper we discuss from an arctic perspective methods and correlation tools that are commonly used to date arctic pleistocene marine and terrestrial events we review the state of the art of arctic geochronology with focus on factors that affect the possibility and quality of dating and support this overview by examples of application of modern dating methods to arctic terrestrial and marine sequences event stratigraphy and numerical ages are important tools used in the arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes age control is commonly provided by radiocarbon luminescence or cosmogenic exposure ages arctic ocean deep sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition patterns in palaeomagnetic records and increasingly biostratigraphic data many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning recent advances in dating technology calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material i e foraminifera for c 14 and single grain luminescence however for much of the pleistocene there are still limits to the resolution of most dating methods consequently improving the accuracy and precision analytical and geological uncertainty of dating methods through technological advances and better understanding of processes are important tasks for the future another challenge is to better integrate marine and terrestrial records which could be aided by targeting continental shelf and lake records exploring proxies that occur in both settings and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

luminescence dating of quaternary sediments in the himalaya and high asia a practical guide to its use and limitations for constraining the timing of glaciation abstract knowledge of the glacial history of high asia is of critical importance for scientific understanding of the palaeoclimate of this region the lack of absolute age controls on glacial landforms of the himalaya and high asia region is arguably the greatest problem facing the construction of a history of quaternary glaciation in these areas a major reason for this lack of dates has been the absence of a suitable dating method this paper reviews the use of optically stimulated luminescence osl dating in the himalaya critical examination of existing data is used to suggest guidelines for the collection of suitable sediments for dating using osl in order to constrain the timing of glaciations osl has been shown to provide reproducible and apparently accurate ages which constrain glacial advances however the correct selection of sediments is of critical importance in spite of developments in the technique there remain limitations to its applicability reasons for this are considered as is the potential of osl for constraining the timing of glacial expansion

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

mis 3 mammoth remains from sweden implications for faunal history palaeoclimate and glaciation chronology the distribution of low arctic megafaunal remains in time and space from the area previously covered by the scandinavian ice sheet sis suggests the presence of breeding mammoth populations in the circum baltic region during the time interval from 44 to 26 ka ago the transport history of 30 mammoth teeth and bones from southern and north central sweden was estimated and the remains were subjected to osteological analyses and 14c dating oxygen isotope analyses of tooth enamel indicate a palaeoclimate considerably more homogenous than that experienced in sweden today showing moderate north south gradients in the d18o value of precipitation and temperature in general the results support the model of restricted ice sheet distribution during the second half of the middle weichselian the clear discrepancy in the inferred absence of glaciation in the central swedish uplands and the baltic basin as evidenced by the swedish mammoth data versus the danish osl based glaciation chronology in the period from 40 to 30 ka ago is discussed in the light of radiocarbon calibration and glacial dynamics r 2007 published by elsevier ltd less

osl ages in central norway support a mis 2 interstadial 25 20 ka and a dynamic scandinavian ice sheet recent work has suggested that the scandinavian ice sheet was much more dynamic than previously believed and its western marine based margin can provide an analogue to the rapid paced fluctuations

volcanic glass as a proxy for cenozoic elevation and climate in the cascade mountains oregon usa abstract after deposition volcanic glass hydrates with ambient water recording the average hydrogen isotope ratio d or 2h of local meteoric water during the hydration period previous researchers have used ancient glass d values to reconstruct paleotopography and paleoclimate while others have questioned the long term reliability of the proxy as a recorder of ancient meteoric water in this study we sampled volcanic glasses ranging in age 33 ma to 1 ma and local meteoric water converted to glass d values throughout the study area we propose a paleoenvironmental interpretation of volcanic glass results that resolves previously published isotopic data and agrees well with the petrologic structural and stratigraphic record namely the oregon cascades have been a significant topographic barrier since at least the mid miocene and likely as far back as the oligocene since reaching a topographic maximum during the eruption of columbia river flood basalts in the mid miocene surface elevations in oregon have decreased while the northern cascades in washington continue to rise

mantle provinces under north america from multifrequency p wave tomography this is a survey of mantle provinces large scale seismic anomalies under north america from the surface down to 1500 1800 km depth the underlying p velocity model was obtained by multifrequency tomography a waveform based method that systematically measures and models the frequency dependence of teleseismic body waves a novel kind of three dimensional rendering technique is used to make the considerable structural complexities under north america accessible in the transition zone and below the north american mantle is dominated by seismically fast provinces which represent distinct subduction episodes of the farallon plate i attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes differences in vertical sinking velocity have led to large vertical offsets across adjacent coeval slabs some of the mantle provinces have not been discussed much previously including 1 a seismically slow blanket overlying the oldest farallon subduction along the eastern continental margin 2 a transition zone slab coeval with the laramide orogeny ca 80 60 myr which i discuss in analogy to the stagnant slab subduction style commonly found in the western pacific today 3 the lower mantle root of present day cascadia subduction which may have started out as intraoceanic subduction 4 a lower mantle slab under arizona and new mexico the last material to subduct before strike slip motion developed along the san andreas boundary and 5 two narrow plate tears thousands of kilometers long one of which is the subducted conjugate of the mendocino fracture zone

on modeling the thermal evolution of the oceanic upper mantle an assessment of the cooling plate model the plate cooling model for the thermal evolution of the oceanic upper mantle has been widely accepted to explain observed variations of depth to oceanic basement and conductive heat flow with the age of the seafloor several estimates of best fitting plate model parameters derived from depth heat flow and age data have been proposed but the viability of the plate model itself has not been rigorously evaluated we have used published mean depths and depths to basement at deep sea drilling project ocean drilling program dsdp odp drilling sites to test the plate cooling model based on two criteria first viable plate models must have coefficients that are consistent with the slope of the corresponding root t line because the half space or root t subsidence of young seafloor is implicit in the plate model i e the slope of the root t line can be calculated directly from the coefficients of the plate subsidence model second any viable physical model must fit the data with an acceptable degree of systematic misfit large systematic misfits indicate that the model cannot explain the observations fits of half space root t models to depth versus age data for young 80 ma seafloor indicate basal temperatures in the range 1300 to 1370 c based on the age at which the depths deviate from the root t line the minimum plate thickness that is compatible with the best fitting half space models for young seafloor is 120 km in contrast all best fitting plate models yield systematically higher temperatures 1450 to 1470 c and thinner plates 102 118 km the plate model can explain the depth to basement at dsdp odp drill sites with a satisfactory degree of systematic misfit but we find that there is no plate cooling model that can explain the variation of the mean depths derived from the dbdb5 database with age over the entire range of ages 0 to 165 ma models that best fit the entire data set have unacceptably large systematic misfits over the entire range of seafloor age whereas models that minimize the systematic misfit for young seafloor 0 to 81 ma fail for older seafloor the plate model clearly fails to explain the observations the cooling history of old seafloor is not simply an extension of the cooling history of young seafloor according to a simple plate cooling model previous studies have suggested as an alternative to the plate model that observed variations of basement depth with age are best explained by the combined effects of a normal half space cooling process and the dynamic and or thermal effects of hot spots or mantle plumes our results are entirely consistent with the half space cooling model and we find that the best reference model for normal subsidence is d t 2600 20 m 345 3 m m y t we also find that the heat flow predicted by this half space model is consistent with the most reliable average heat flow values from the pacific

paleobotanical evidence of eocene and oligocene paleoaltitudes in midlatitude western north america comparisons of the physiognomy of leaves from modern vegetation of known climates with that of eocene and oligocene fossil leaf assemblages from middle latitudes of western north america indicate paleoaltitudes comparable or higher than those at present using canonical correspondence analysis a multivariate statistical approach that includes nonlinear relationships between characters and environmental parameters we relate leaf physiognomy of fossil samples to modern vegetation of known environmental parameters including moist enthalpy of the atmosphere a thermodynamically conserved quantity of the atmosphere that varies with altitude by estimating enthalpy values for both lowland leaf assemblages and coeval interior leaf assemblages altitudes for the interior assemblages can be estimated to 890 m in northeastern washington and southern british columbia the high eocene altitudes indicate subsidence or collapse of an area undergoing crustal extension and may reflect an immediately preceding period of uplift that triggered the extension similarly other areas that have undergone cenozoic crustal extension appear to have been at least as high as they are at present three sites from the rocky mountains also indicate elevations at least as high as at present and therefore suggest subsidence either resulting from cooling of a hot upper mantle or erosion and isostatic compensation of surrounding terrain high altitudes during eocene and oligocene time in western north america appear to have been normal even in areas such as the green river basin and therefore cast doubt on the commonly inferred late cenozoic uplift of that region

origins of topography in the western u s mapping crustal and upper mantle density variations using a uniform seismic velocity model to investigate the physical basis for support of topography in the western u s we construct a subcontinent scale 3 d density model using 1000 estimated crustal thicknesses and s velocity profiles to 150 km depth at each of 947 seismic stations crustal temperature and composition are considered but we assume that mantle velocity variations are thermal in origin from these densities we calculate crustal and mantle topographic contributions typical 2 uncertainty of topography is 500 m and elevations in 84 of the region are reproduced within error remaining deviations from observed elevations are attributed to melt variations in crustal quartz content and dynamic topography compositional variations in the mantle while plausible are not necessary to reproduce topography support for western u s topography is heterogeneous with each province having a unique combination of mechanisms topography due to mantle buoyancy is nearly constant within 250 m across the cordillera relief there 2 km results from variations in crustal chemistry and thickness cold mantle provides 1 5 km of ballast to the thick crust of the great plains and wyoming craton crustal temperature variations and dynamic pressures have smaller magnitude and or more localized impacts positive gravitational potential energy gpe anomalies 2 1012n m calculated from our model promote extension in the northern basin and range and near the sierra nevada negative gpe anomalies 3 1012n m along the western north american margin and yakima fold and thrust belt add compressive stresses stresses derived from lithospheric density variations may strongly modulate tectonic stresses in the western u s continental interior

palinspastic restoration of navdat and implications for the origin of magmatism in southwestern north america 1 simultaneous palinspastic restoration of deformation and volcanism illuminates relationships between magmatism and tectonics in western north america using arcgis we retrodeformed the navdat north american volcanic database navdat geongrid org using the western north america reconstruction of mcquarrie and wernicke 2005 from these data sets we quantitatively compare rates of magmatism and deformation and evaluate the age composition and migration of cenozoic volcanism from 36 ma to present these relationships are shown in a series of palinspastic maps as well as animations that highlight migrating extension and volcanism with time western north america is grouped into eight different regions with distinct relationships between strain and volcanism to evaluate competing hypotheses regarding the relationship of extension to continental magmatism a first order observation from this study is that magmatism throughout the basin and range appears to be primarily driven by plate boundary effects notably subducting and foundering slabs as well as slab windows exceptions include the yellowstone hotspot system along the northern border of our study area and late stage 8 ma passive extension related asthenospheric upwelling along the eastern and western margins of the basin and range the palinspastic reconstructions presented here highlight that the classic high angle basin and range faulting that comprises most of the physiographic basin and range province commenced during a magmatic lull more broadly with the exception of the rio grande rift we find that pulses of magmatism lag the onset of extension these observations largely contradict the active rifting model where magmatism triggers basin and range extension

zeroing of the tl signal in sediment undergoing fluvioglacial transport an example from austerdalen western norway abstract study of levels of natural tl in sediment undergoing fluvial transport in austerdalen norway shows that bleaching does occur but does not follow a regular pattern this is attributed to the incorporation of older unbleached material into the sediment load as a result of riverbank erosion levels of residual tl are high enough to raise doubts about the accuracy of fine grain tl dating of fluvioglacial sediments which have experienced only a short distance of transport

spatial and temporal variation of cenozoic surface elevation in the great basin and sierra nevada the surface uplift of mountain belts caused by tectonism plays an important role in determining the long term climate evolution of the earth however the general lack of information on the paleotopography of mountain belts limits our ability to identify the links and feedbacks between topography tectonics and climate change on geologic time scales here we present a 1 8 o and d record of authigenic minerals for the northern great basin that captures the timing and magnitude of regional surface uplift and subsidence events in the western united states during the cenozoic authigenic calcite smectite and chert 1 8 o values suggest the northern great basin region experienced 2km of surface uplift between the middle eocene and early oligocene followed by 1 to 2km of surface subsidence in the southern great basin and or sierra nevada since the middle miocene these data when combined with previously published work show that the surface uplift history varied in both space and time surface uplift migrated from north to south with high elevations in southern british columbia and northeastern washington in the middle eocene and development of surface uplift in north and central nevada in the oligocene this pattern of north to south surface uplift is similar to the timing of magmatism in the western cordillera a result that supports tectonic models linking magamtism with removal of mantle lithosphere and or a subducting slab

palaeoenvironments in the southern baltic sea basin during marine isotope stage 3 a multi proxy reconstruction abstract sediment cores from kriegers flak in the southwestern baltic sea provide a unique possibility to study the middle weichselian history of the baltic basin three weichselian interstadial units have been identified and are attributed to marine isotope stage 3 mis 3 60 25 ka the oldest unit a is characterized by a deglaciation sequence gradually turning into brackish water clay the low diversity benthic foraminiferal fauna stable oxygen isotope values and mg ca ratios indicate low temperature and salinity for unit a a hiatus separates unit a from the overlying unit b which was deposited in wetlands and shallow lakes between 42 and 36 cal ka bp macrofossil and pollen analyses indicate deposition of unit b in an area dominated by a tree less open tundra environment possibly with some birch and pine in sheltered positions the uppermost unit c is characterized by clay deposition including redeposition of material from older sediments unit b optically stimulated luminescence osl ages indicate deposition of unit c between 26 and 28 5 ka radiocarbon ages of 39 and 40 cal ka bp for unit c are considered to be too old the following depositional model is suggested i isostatic depression of the region after an advance of the scandinavian ice sheet sis most likely the ristinge ice advance previously dated to c 55 50 ka enabled an inflow of marine waters into the baltic basin during the deposition of unit a ii isostatic rebound caused a regression at kriegers flak and a hiatus between units a and b iii wetlands and smaller lakes formed in the uplifted area between 42 and 36 cal ka bp unit b iv deposition of glaciolacustrine clays at kriegers flak demonstrates that a growing sis dammed kattegat and the baltic basin c 28 5 to 26 ka the new evidence from kriegers flak provides a solid framework for future mis 3 palaeoenvironmental reconstructions in the circum baltic area

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

segmentation of the farallon slab abstract recent tomography images reveal a complex 3d mantle structure beneath western united states with feature morphology varying rapidly with depth by assimilating plate motion history paleo age of sea floor and paleo geography of plate boundaries in a 3 d numerical model we simulate the farallon juan de fuca subduction during the past 40 ma we find that the highly segmented upper mantle structure of western u s is a direct result of the farallon subduction we show that the tilted horseshoe shaped fast seismic anomaly beneath nevada and utah at 300 600 km depth range is in fact a segment of curled slab subducted since 15 ma and the shallower linear slab beneath the cascades is younger than 5 ma the distinct morphology between these two parts of the subduction system indicates the strong influence of the fast trench rollback since 20 ma the northward migrating jf pa na triple junction and the toroidal flow around slab edges the observed mantle structures are used to constrain the rheology of the upper mantle through matching the shape depth and location of modeled subducted slab segments the inferred viscosity for the asthenosphere is 5 10 19 pa s and those for the transition zone and lower mantle are 1 5 10 21 pa s and 2 10 22 pa s respectively the slab is found to be about 2 orders of magnitude stronger than the ambient mantle above 410 km depth but of similar order of magnitude viscosity in the transition zone

mantle dynamics isostasy and the support of high terrain dynamic topography is commonly understood to be deflection of the earth s surface that results from convection of the mantle because different authors use the words dynamic topography differently topography designated as dynamic may amount to only a few hundred meters or may exceed 2000 m for most regions however surface heights computed on the assumption that the lithospheric column is in isostatic equilibrium provide good approximations to observed topography the small free air gravity anomalies and still smaller isostatic anomalies 2000 m of dynamic topography moreover simple examples show that if flow induced stresses maintain a given density distribution then the resultant surface deflections can be smaller than those that would exist in isostatic equilibrium in light of confusion over the term dynamic topography we offer readers simple tools that we hope will enable them to diagnose the component of topography that results from flow induced stresses and to distinguish it from topography that is compensated isostatically

western u s seismic anisotropy revealing complex mantle dynamics abstract the origin of the complex pattern of sks splitting over the western united states u s remains a long lasting debate where a model that simultaneously matches the various sks features is still lacking here we present a series of quantitative geodynamic models with data assimilation that systematically evaluate the influence of different lithospheric and mantle structures on mantle flow and seismic anisotropy these tests reveal a configuration of mantle deformation more complex than ever envisioned before in particular we find that both lithospheric thickness variations and toroidal flows around the juan de fuca slab modulate flow locally but their co existence enhances large scale mantle deformation below the western u s the ancient farallon slab below the east coast pulls the western u s upper mantle eastward spanning the regionally extensive circular pattern of sks splitting the prominent e w oriented anisotropy pattern within the pacific northwest reflects the existence of sustaining eastward intrusion of the hot pacific oceanic mantle to beneath the continental interior from within slab tears below oregon to under the snake river plain and the yellowstone caldera this work provides an independent support to the formation of intra plate volcanism due to intruding shallow hot mantle instead of a rising mantle plume

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

optical dating studies of quartz and feldspar sediment extracts abstract continuing developmental work into optical dating has led to some clarification of the optical behaviour of quartz and feldspar sediment extracts we have verified the key assumption intrinsic to the method that the optical signal is zeroed completely upon exposure to daylight we also show that the rate of zeroing in optical dating is much more rapid than it is in tl dating studies concerned with the extraction of the thermally stable signal from laboratory irradiated samples showed that problems may arise from medium to high temperature preheating of young samples optical alternatives to thermal stabilization were tested using dye and krypton lasers using a krypton laser we have succeeded in obtaining an equivalent dose of 0 0 0 7 gy for the quartz from a modern intertidal sand and an average dose of 120 22 gy for the feldspar extract of a 70 ka sand unit both were obtained using six wavelengths from the infrared to the violet and no dependence on wavelength was found we found that the photon energies of infrared and deep red light can stimulate luminescence in unirradiated quartz and feldspar extracts of sediments this was not expected and suggests that the process of trap emptying is more complex than we had envisioned but implies a far greater than expected degree of technical flexibility for the optical dating method

topographic evolution of the western united states since the early miocene abstract the origin of the high topography within the western united states has been attributed to either crustal lithospheric isostasy or dynamic topography but their relative contributions remain unconstrained here we investigate this problem using gravity residual topography and geodynamic modeling we first evaluate two end member scenarios of isostatic balance crustal isostasy and lithospheric isostasy both cases lead to prominent negative mantle residual gravity within the tectonically active western u s and unrealistic crustal lithospheric density structures requiring the presence of low density mantle underneath the negative mantle residual gravity is consistent with both the estimated positive residual topography and calculated dynamic uplift due to the presence of hot asthenospheric mantle underneath geodynamic modeling further reveals that this landward migrating dynamic uplift originates from the eastward intrusion of the hot pacific mantle through tears and edges of the juan de fuca slab since middle miocene the estimated paleotopography maps by combining dynamic topography and lithosphere isostasy over the western u s are consistent with several observational constraints including episodic uplifts of the sierra nevada post mid miocene uplift of the idaho batholith the sustaining subsidence within most of the b r and the largely stable topography of central colorado plateau since 20 ma

application of ground penetrating radar to investigation of near surface fault properties in the san francisco bay region abstract in many geologic environments ground penetrating radar gpr provides high resolution images of near surface earth structure gpr data collection is nondestructive and very economical the scale of features detected by gpr lies between those imaged by high resolution seismic reflection surveys and those exposed in trenches and is therefore potentially complementary to traditional techniques for fault location and mapping sixty two gpr profiles were collected at 12 sites in the san francisco bay region results show that gpr data correlate with large scale features in existing trench observations can be used to locate faults where they are buried or where their positions are not well known and can identify previously unknown fault segments the best data acquired were on a profile across the san andreas fault traversing pleistocene terrace deposits south of olema in marin county this profile shows a complicated multi branched fault system from the ground surface down to about 40 m the maximum depth for which data were recorded

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

dynamic subsidence and uplift of the colorado plateau we use inverse models of mantle convection to explore the vertical evolution of the colorado plateau by satisfying multiple constraints seismic tomography stratigraphy in the western united states and great plains and other structural and volcanic data adjacent to the plateau the model provides predictions on the continuous history of colorado plateau vertical motion since 100 ma with the arrival of the flat lying farallon slab dynamic subsidence swept from west to east over the plateau and reached a maximum ca 86 ma two stages of uplift followed the removal of the farallon slab below the plateau one in the latest cretaceous and the other in the eocene with a cumulative uplift of 1 2 km both the descent of the slab and buoyant upwellings raised the plateau to its current elevation during the oligocene a locally thick plateau lithosphere enhances the coupling to the upper mantle so that the plateau has a higher topography with sharp edges the models predict that the plateau tilted downward to the northeast before the oligocene caused by northeast trending subduction of the farallon slab and that this northeast tilting diminished and reversed to the southwest during the miocene in response to buoyant upwellings

oceanic residual topography agrees with mantle flow predictions at long wavelengths dynamic topography the surface deflection induced by sublithosheric mantle flow is an important prediction made by geodynamic models but there is an apparent disparity between geodynamic model predictions and estimates of residual topography total topography minus lithospheric and crustal contributions we generate synthetic global topography fields with different power spectral slopes and spatial patterns to investigate how well the long wavelength spherical degrees 1 to 3 components can be recovered from a discrete set of samples where residual topography has been recently estimated an analysis of synthetic topography along with observed geoid and gravity anomalies demonstrates the reliability of signal recovery appropriate damping factors which depend on the maximum degree in the spherical harmonic expansion that is used to fit the samples must be applied to recover the long wavelength topography correctly large damping factors smooth the model excessively and suppress residual topography amplitude and power spectra unrealistically recovered long wavelength residual topographies based on recent oceanic point wise estimates with different spherical expansion degrees agree with each other and with the predicted dynamic topography from mantle flow models the peak amplitude of the long wavelength residual topography from oceanic observations is about 1 km suggesting an important influence of large scale deep mantle flow

drumlinised glaciofluvial and glaciolacustrine sediments on the smaland peneplain south sweden new information on the growth and decay history of the fennoscandian ice sheets during mis 3 abstract dug trenches in sediment cored drumlins on the smaland peneplain southern sweden occurring intermixed with rock cored drumlins revealed sedimentary successions and facies suggesting that the core sediments were primarily deposited proglacially both in glaciolacustrine settings as delta front and more distal deeper water sediments and as glaciofluvial braidplain sediments from the relationship between the drumlin sorted sediment cores and their surficial drape by a till carapace it is concluded that erosion was the main drumlin forming process here reshaping the original sediment morphology into streamlined landforms after which a more or less thick traction till was deposited over the eroded and or deformed ice bed interface drumlin formation probably took place during the last deglaciation over the area the drumlin core sediments in 14 excavated trenches were dated by optically stimulated luminescence osl most retrieved ages fall into two distinct groups both within marine isotope stage 3 c 60 30 ka when plotted as mean osl ages for each site all but two sites fall either into an older age group c 48 56 ka seven sites or into a younger age group c 28 38 ka five sites these age intervals correlate well with the suggested time spans for the ristinge and klintholm ice advances in denmark by ice flowing from the baltic basin westwards terminating in fan shaped patterns these interstadial ice advances in the southwestern sector of the fennoscandian ice sheet give rise to enigmatic questions on the physics and mechanics of ice sheet build up and decay especially as palaeoenvironmental data for northern fennoscandia suggest widespread ice free conditions within roughly the same time fame as the recorded ice advances in the south

melt out till and ribbed moraine formation a case study from south sweden abstract hummocky moraine with dispersed agglomerations of ribbed moraine here named asnen type ribbed moraine forms a 20 40 km wide zone over smaland south sweden terminated to the north by a sharp boundary to streamlined terrain the hummocky ribbed moraine zone can be geomorphologically linked to the subaqueous goteborg moraine formed at an oscillation stand still phase during the deglaciation of the swedish west coast based on detailed sedimentological and structural investigations of ribbed moraine ridges it is concluded that diamict sequences and associated sorted sediment were deposited due to passive melt out from stagnant debris rich ice with synsedimentary deposition of sorted sediments preferentially at a melting ice bed interface to accommodate for the geomorphological expression such an interpretation further implies that debris rich ice formed in an intermediate adfreezing zone between ice at the pressure melting point and a frontal frozen zone at deglaciation basal debris rich ice was stacked into transversally arranged zones controlled moraine forming ribbed moraine embryos the active phase of ridge formation the stacked sequences of debris rich ice eventually melted out beneath a stable and melt retarding supraglacial ablation complex to form the final moraine ridges the passive phase of ridge formation in areas with no stable supraglacial ablation complex the resulting landform after final de icing was a hummocky moraine landscape internal composition of moraine hummocks suggests that most of them are composed of sediment gravity flow sediments intercalated with stream deposited sediments all resting on a platform of subglacial melt out till de icing of the zone now occupied by hummocky and ribbed moraine took a considerable time deglacial 14 c age differences from lake basins on either side of the geomorphic boundary to the streamlined terrain indicate a separation between active and stagnant ice along that boundary and that it took another 200 300 yr for the stagnant ice zone to melt during the final formation of present day landforms

osl dating of middle weichselian age shallow basin sediments in western latvia eastern baltic abstract this paper presents the results of the first attempt to date the quaternary sediments of western latvia in the southeast baltic region using luminescence the analyses have been carried out on sandy sediments of the jurkalne formation that are located between upper and lower scandinavian sourced tills previous publications on the origin of the quaternary sediments in the region are reviewed and it is found that there are a wide range of explanations for their processes of formation and their age of formation it is concluded that although the sandy sediments were deposited in freshwater environment although they contain both marine and freshwater fauna and flora a property that is explained by derivation and glaciotectonic deformation and mixing the samples used for dating were collected from surface exposures and boreholes and yield results that range in age from 52 10 ka bp to 26 4 1 ka bp as a result of this study it is suggested that the dated sediments were deposited in a freshwater basin during mis 3 and are overlain by a till deposited by scandinavian ice during the late weichselian mis 2 lgm the underlying till is attributed to a middle weichselian glaciation and tentative suggestions are presented for the age of other deposits that underlie the dated sediment

preglacial surface remnants and quaternary glacial regimes in northwestern sweden abstract we present a detailed map of the distribution of preglacial surface remnants in the kebnekaise region of northwestern sweden in this mountain area we discern four important large scale geomorphological units each representing a specific set of erosional agents and formative conditions these are i intact preglacial surface remnants characterized by gentle slopes round summits wide shallow valleys and an absence of rock basins ii preglacial surface remnants showing signs of minor glacial erosion and deposition iii glacially scoured surfaces including glacial troughs iv deep fluvial valleys cut into the preglacial surface the pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120 000 years and inferred to have repeatedly prevailed during the last 2 75 million years cirque glaciation mountain ice sheets and fennoscandian ice sheets a deep ocean oxygen isotope record of foraminifera from the north atlantic dsdp 607 was used to infer the temporal extent of these modes of glaciation during the last 2 75 million years we interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration the basal thermal regime and the duration of such glaciation events the average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys where outlet glaciers and ice streams formed the pre glacial landscape is best preserved at intermediate elevations low enough not to have been covered by cirque glaciers and apparently high enough not to have experienced melted bed conditions and subglacial erosion during ice sheet overriding events in a narrow high relief zone along the elevation axis interglacial fluvial erosion was morphologically important the absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice free interval in contrast no persistent fluvial valley pattern could develop in zones subjected to repeated glacial scouring and hence derangement of fluvial patterns

deep mantle contributions to the surface dynamics of the north american continent abstract the regional and continental scale dynamics of north america and vicinity are explored using a high resolution model of mantle flow the model is constrained by simultaneously inverting global seismic and mantle convection data sets and it includes an explicit treatment of the positive chemical buoyancy of the continental tectosphere moreover it adopts a depth dependent mantle viscosity structure which reconciles both glacial isostatic adjustment gia and convection data the flow model successfully reproduces plate velocities and observations of surface gravity and topography including the continent scale quasi linear depression after corrections for gia and crustal heterogeneity extending from northern alaska to venezuela the predictions also match lithospheric flow and stress fields inferred from local and regional measurements of seismic anisotropy and surface deformation we demonstrate that these signals are largely driven by viscous flow coupled to density anomalies in the deep portions of the upper mantle and within the lower mantle where the latter may be associated with the descent of the ancient kula farallon plate system and an active mantle upwelling below the pacific margin of the north american plate more importantly the flow calculations elucidate how these large scale heterogeneities give rise to regional scale flow and stress patterns below the southwestern u s and below the central u s

p and s wave tomography of the mantle beneath the united states mantle seismic structure beneath the united states spanning from the active western plate margin to the passive eastern margin was imaged with teleseismic p and s wave traveltime tomography including usarray data up to may 2014 to mitigate artifacts from crustal structure 5 40 s rayleigh wave phase velocities were used to create a 3 d starting model major features of the final p and s models include two distinct low velocity anomalies at depths of 60 300 km beneath the central and northern appalachians and passive margin the central appalachian low velocity anomaly coincides with eocene basaltic magmatism and the northern anomaly is located along the cretaceous track of the great meteor hot spot at depths of 300 700 km beneath the central and eastern u s large high velocity anomalies are inferred to be remnants of the farallon slab that subducted prior to 40 ma during the laramide orogeny

a hybrid approach to data assimilation for reconstructing the evolution of mantle dynamics quantifying past mantle dynamic processes represents a major challenge in understanding the temporal evolution of the solid earth mantle convection modeling with data assimilation is one of the most powerful tools to investigate the dynamics of plate subduction and mantle convection although various data assimilation methods both forward and inverse have been created these methods all have limitations in their capabilities to represent the real earth pure forward models tend to miss important mantle structures due to the incorrect initial condition and thus may lead to incorrect mantle evolution in contrast pure tomography based models cannot effectively resolve the fine slab structure and would fail to predict important subduction zone dynamic processes here we propose a hybrid data assimilation approach that combines the unique power of the sequential and adjoint algorithms which can properly capture the detailed evolution of the downgoing slab and the tomographically constrained mantle structures respectively we apply this new method to reconstructing mantle dynamics below the western u s while considering large lateral viscosity variations by comparing this result with those from several existing data assimilation methods we demonstrate that the hybrid modeling approach recovers the realistic 4 d mantle dynamics the best

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

timing and east west correlation of south swedish ice marginal lines during the late weichselian abstract the retreat of the late weichselian ice sheet over the southern part of sweden is marked along the southwest coast by distinct marginal moraine ridges their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines along the southeastern side of the peninsula the ice recession has been reconstructed based on a combination of clay varve chronology pollen and radiocarbon stratigraphy a morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west coast moraines cannot be followed through the central part of the peninsula towards the east coast this paper is an attempt to reconstruct an age equivalent west east extension of the ice recession lines on the basis of existing data sets for our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon dated clay varve chronology on the east coast we conclude that the two oldest moraines on the west coast formed at 18 000 16 000 and 15 400 14 500 cal yr bp respectively during the following rapid deglaciation which may have coincided with the beginning of the bolling pollen zone large parts of southernmost sweden became ice free except for higher elevated areas where stagnant ice remained for another 400 500 yr a best guess is that the formation of the next younger ice marginal lines may have occurred at 14 400 14 200 14 200 and 13 400 cal yr bp and during the younger dryas cold event

problems and potential of osl dating weichselian and holocene sediments in sweden recent osl dating of various late quaternary deposits in sweden has resulted in several sets of ages that appear inconsistent with geological interpretation they usually overestimate the expected age we explore the problems and potential of osl dating in sweden by analysing quartz osl ages from several known age sites in sweden and by investigating their luminescence properties two difficulties in obtaining accurate and precise ages are incomplete bleaching and low sensitivity quartz incomplete bleaching can give rise to age overestimation but the importance of this effect can be minimised by selecting suitable sediment facies although for some settings unexplained overestimates still remain low quartz osl sensitivity leads to practical problems in measurements and larger uncertainties in dose estimates but not necessarily to systematic age overestimation sites that contain dala sandstone clasts and or sediments that may have had extensive reworking during the quaternary seem to provide high sensitivity quartz we consider such sites to show the most potential for accurate and precise osl dating in sweden

western us volcanism due to intruding oceanic mantle driven by ancient farallon slabs the origin of late cenozoic intraplate volcanism over the western united states is debated one important reason is the lack of a clear understanding of the mantle dynamics during this volcanic history here we reconstruct the mantle thermal states beneath north america since 20 million years ago using a hybrid inverse geodynamic model with data assimilation the model simultaneously satisfies the past subduction kinematics present mantle tomographic image and the volcanic history we find that volcanism in both the yellowstone volcanic province and the basin and range province corresponds to a similar eastward intruding mantle derived from beneath the pacific ocean and driven mostly by the sinking farallon slab below the central eastern united states the hot mantle that forms the columbia river flood basalt and subsequent yellowstone newberry hotspot tracks first enters the western united states through tears within the juan de fuca slab subsequent coexistence of the westward asthenospheric flow above the retreating juan de fuca slab and eastward propagating mantle beyond the back arc region reproduces the bifurcating hotspot chains a similar but weaker heat source intrudes below the basin and range around the southern edge of the slab and can explain the diffuse basaltic volcanism in this region according to our models the putative yellowstone plume contributes little to the formation of the yellowstone volcanic province volcanism in the western us may result from warm oceanic mantle beneath the pacific ocean being drawn eastwards by mantle flow induced by the sinking of farallon slabs according to numerical model simulations

timing of the late vistulian weichselian glacial phases in poland abstract the lower vistula region in northern poland is a stratotype area for the vistulian weichselian glaciation and during last glacial maximum lgm the southernmost extension of the scandinavian ice sheet occurred in western poland and in eastern germany reinterpretation of the available geochronological data radiocarbon 36 cl and 10 be ages supplied with new field geological evidence mostly for the late vistulian ice sheet limits and movement directions was focused in three key regions in poland during the late middle vistulian there was one or two ice sheet advances in the lower vistula region the late vistulian maximum ice sheet limit in poland was time transgressive and occurred at 24 19 kyrs bp generally the younger to the east ice sheet limits during the leszno phase occurred at 24 cal 10 be 36 cl kyrs the poznan phase ice sheet limit was dated to 19 10 be 36 cl kyrs and the pomeranian phase ice sheet limit about 16 17 10 be 36 cl kyrs every late vistulian glacial phase in poland was preceded by an ice sheet retreat

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

late weichselian environmental history in southeastern sweden during the deglaciation of the scandinavian ice sheet abstract late weichselian litho bio and chronostratigraphy 14 c and varves in southeastern sweden provide a detailed picture of the deglaciation pattern and dynamics shore displacement late glacial sedimentation and history of the landscape vegetation and climate two plausible glacial models were tested against lithologic chronologic and climatic data permafrost at and outside the ice margin and topographic conditions beneath the ice apparently caused inward spread of frozen glacier bed conditions this led to a buildup of a large zone of debris rich basal ice a climatic amelioration about 12 700 yr b p changed the temperature profile in the ice sheet deposition of basal melt out till began at the previously frozen glacier bed and a rapid recession of the clean ice set in thin exposed debris rich basal ice which was separated from the active ice margin about 150 yr later in this zone of stagnant ice there followed a 200 300 yr period marked by subglacial and supraglacial melt out and resedimentation forming a large hummocky transverse moraine the mild climate favored rapid plant immigration and a park tundra was established the gradual closing of the landscape was interrupted by a 100 to 150 yr period of tundra vegetation and a cool dry climate with local vegetational differences caused by differences in soil moisture about 12 000 yr b p a second climatic amelioration set in and during the next 1000 yr a birch and pine woodland gradually developed soils stabilized and empetrum heaths became abundant as the climate gradually deteriorated at the end of this period by 11 000 yr b p the area had become a tundra again with scattered birch stands dominated by herbs such as artemisia chenopodiaceae grasses and sedges some 500 yr later a birch pine woodland again succeeded and within about 500 yr the vegetation changed to a rather closed woodland as the climate ameliorated further however the time lag between climatic and vegetation change was considerable

static and dynamic support of western united states topography article history accepted 7 october 2013 available online 31 october 2013 editor p shearer isostatic and dynamic models of earth s surface topography can provide important insights into the driving processes of tectonic deformation we analyze these two estimates for the tectonically active western united states using refined structural models derived from earthscope usarray for the crust use of recent moho depth measurements and crustal density anomalies inferred from passive source seismology improve isostatic models however seismically determined lithospheric thickness variations from lithosphere asthenosphere boundary lab maps and lithospheric and mantle density anomalies derived from heat flow or uppermost mantle tomography do not improve isostatic models substantially perhaps this is a consequence of compositional heterogeneity a mismatch between thermal and seismological lab and structural complexity caused by smaller scale dynamics the remaining non isostatic dynamic component of topography is large topography anomalies include negative residuals likely due to active subduction of the juan de fuca plate and perhaps remnants of formerly active convergence further south along the margin our finding of broad scale positive residual topography in the basin and range substantiates previous results implying the presence of anomalous buoyancy there which we cannot fully explain the colorado plateau does not appear dynamically anomalous at present except at its edges many of the residual topography features are consistent with predictions from mantle flow computations this suggests a convective origin and important interactions between vigorous upper mantle convection and intraplate deformation