paleoaltimetry from stable isotope compositions of fossils stable isotope systematics of phosphatic vertebrate and carbonate invertebrate fossils are reviewed emphasizing external vs biological controls on isotope compositions and their variation external controls include elevation and isotopic lapse rates temperature atmospheric circulation patterns aridity and changes to precipitation seasonality e g development of monsoons biological controls include temperature regulation and temperature dependent biological activity water balance behavior and rates of hard part secretion and maturation some key factors include what sources of water an animal samples how those sources respond isotopically to elevation and the isotopic sensitivity of a biologic tissue to environmental changes general research design criteria are enumerated including numbers of fossils and analyses required as well as uncertainties in the interpretability of isotopic shifts isotope zoning from fossil teeth and shells from the indian foreland demonstrate comparable seasonal monsoon signals at 11 ma vs today implying a high and broad plateau at that time mean isotope compositions of fossil teeth from the lee of the cascade range central oregon show a pronounced decrease in 18 o initiating 7 ma signaling topographic rise associated with impingement of basin and range extension on the arc mean compositions and zoning in fossil shells from the northern rocky mountains indicate high elevations and topographic relief in the late cretaceous and early paleogene paleoaltimetry will principally benefit from better estimates of temperature because temperature lapse rates are less variable than isotopic lapse rates and because the combination of temperature and isotopic studies may help distinguish between local isotopic changes and distal ones caused by catchment or rain shadow effects

constant elevation of southern tibet over the past 15 million years the uplift of the tibetan plateau an area that is 2 000 km wide to an altitude of about 5 000 m has been shown to modify global climate and to influence monsoon intensity mechanical and thermal models for homogeneous thickening of the lithosphere make specific predictions about uplift rates of the tibetan plateau but the precise history of the uplift of the plateau has yet to be confirmed by observations here we present well preserved fossil leaf assemblages from the namling basin southern tibet dated to approximately 15 myr ago which allow us to reconstruct the temperatures within the basin at that time using a numerical general circulation model to estimate moist static energy at the location of the fossil leaves we reconstruct the elevation of the namling basin 15 myr ago to be 4 689 895 m or 4 638 847 m depending on the reference data used this is comparable to the present day altitude of 4 600 m we conclude that the elevation of the southern tibetan plateau probably has remained unchanged for the past 15 myr

impact of particle shape on saltating mode of bedload transport sheared by turbulent flow abstractthe saltating mode of sediment transport is the dominant mechanism of bedload transport in a fluvial stream especially in mountainous rivers in most simulation studies the actual shapes

empirical relationship between leaf wax n alkane δd and altitude in the wuyi shennongjia and tianshan mountains china implications for paleoaltimetry article i nfo estimating past elevation not only provides evidence for vertical movements of the earth s lithosphere but also increases our understanding of interactions between tectonics relief and climate in geological history development of biomarker hydrogen isotope based paleoaltimetry techniques that can be applied to a wide range of sample types is therefore of continuing importance here we present leaf wax derived n alkane d dwax values along three soil altitudinal transects at different latitudes in the wuyi shennongjia and tianshan mountains in china to investigate dwax gradients and the apparent fractionation between leaf wax and precipitation ewax p we findthatsoil dwax trackaltitudinal variationsof precipitation d along the three transects that span variable environment conditions and vertical vegetation spectra an empirical dwax altitude relation is therefore established in which the average dwax lapse rate of 2 27 0 38 100 m is suitable for predicting relative paleoelevation change relative uplift the application of this empirical gradient is restricted to phases in the mountain uplift stage whenthe atmospheric circulation had not distinctly changed and to when the climate was notarid anempirical dwax latitude altitudeformulaisalsocalculated dwax 3 483lat 0 0227alt 261 5 which gives the preliminary spatial distribution pattern of dwax in modern china meanvalue of ewax p intheextreme humid wuyimountainsisquite negative 154 compared to the humid shennongjia 129 and the arid but with abundant summer precipitation tianshan mountains 130 which suggests aridity or water availability in the growing season is the primary factor controlling soil sediment ewax p along the tianshan transects values of ewax p are speculated to be constant with altitude while along the wuyi and shennongjia transects ewax p are also constant at the low mid altitudes but become slightly more negative at high altitudes which could be attributed to overestimates of precipitation d or the vegetation shift to grass conifer additionally a reversal of altitude effect in the vertical variation of dwax was found in the alpine zone of the tianshan mountains which might be caused by atmospheric circulation change with altitude this implies that the paleo circulation pattern and its changes should alsobe evaluated whenstable isotope based paleoaltimetry is applied

experiments on saltation of sand in water a high speed video system was used to study saltation of sand in an open channel flow high rates of image acquisition provided the information needed to resolve details of the lagrangian properties of particle motion saltation of sand is described in terms of statistical properties of particle trajectories such as mean values and standard deviations of saltation length height and streamwise particle velocity results are compared with available empirical data saltation height seems to be independent of particle size when made dimensionless with the particle diameter however the dimensionless saltation length appears to increase as the particle size decreases particle collision with the bed is also analyzed observations of this process indicate that most of the interactions between saltating particles and the bed are of the collision rebound type which contradicts previous discussions on the subject the estimated value of the dynamic friction coefficient is about half that proposed by bagnold i

normal and anomalous diffusion of gravel tracer particles in rivers received 12 december 2008 revised 16 november 2009 accepted 10 december 2009 published 4 may 2010 1 one way to study the mechanism of gravel bed load transport is to seed the bed with marked gravel tracer particles within a chosen patch and to follow the pattern of migration and dispersal of particles from this patch in this study we invoke the probabilistic exner equation for sediment conservation of bed gravel formulated in terms of the difference between the rate of entrainment of gravel into motion and the rate of deposition from motion assuming an active layer formulation stochasticity in particle motion is introduced by considering the step length distance traveled by a particle once entrained until it is deposited as a random variable for step lengths with a relatively thin e g exponential tail the above formulation leads to the standard advection diffusion equation for tracer dispersal however the complexity of rivers characterized by a broad distribution of particle sizes and extreme flood events can give rise to a heavy tailed distribution of step lengths this consideration leads to an anomalous advection diffusion equation involving fractional derivatives by identifying the probabilistic exner equation as a forward kolmogorov equation for the location of a randomly selected tracer particle a stochastic model describing the temporal evolution of the relative concentrations is developed the normal and anomalous advection diffusion equations are revealed as its long time asymptotic solution sample numerical results illustrate the large differences that can arise in predicted tracer concentrations under the normal and anomalous diffusion models they highlight the need for intensive data collection efforts to aid the selection of the appropriate model in real rivers

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

continuous saltating process of multiple sediment particles the purpose of this study is to investigate the interacting mechanism between the saltating particles near the channel bed a real time flow visualization technique was developed to measure the interparticle collision behaviors during the saltating process a two dimensional continuous saltation model was also developed this model was calibrated and verified with the experimental data collected with satisfactory results the model is able to simulate the continuous saltating trajectories of several particles the simulated maximum saltation height is about 2 2 5 times the values calculated by a single particle saltation model due to the effects of particle collision the simulated saltation velocities of the multiple particles model are less than those derived from a single particle model regression equations for the saltating height and velocity were obtained

paleoelevations in the jianchuan basin of the southeastern tibetan plateau based on stable isotope and pollen grain analyses abstract the southeastern margin of the tibetan plateau tp is a key region for understanding the region s surface uplift mechanisms this study focused on the jiuziyan and shuanghe formations fms in the jianchuan basin both of which include lacustrine calcareous mudstones and marls ostracods of the genus austrocypris found within the jiuziyan and shuanghe fms constrain the age of strata to the late eocene this study used two different proxies i e fossil pollen coexistence and the 18o vpdb values of carbonate 18oc to reconstruct paleoelevation and the extant paleoenvironment from lacustrine calcareous mudstones and marls preserved in the eocene stratigraphy of the jianchuan basin the coexistence approach ca using pollen data from the shuanghe fm indicates a paleoelevation of 1 3 2 6 km above sea level asl which would most probably have been associated with a vegetation cover consisting of tropical subtropical deciduous coniferous broadleaf forests the reconstructed mean annual air temperature maat had a value of 16 8 21 7 c warmer than today s maat 6 c oxygen isotope results from the jiuziyan fm with without modification between eocene and modern myanmar sea level suggested that the surface of the jianchuan basin was at a paleoelevation between 0 5 0 8 0 5 km asl and 2 5 0 7 km asl 18omw 8 9 1 3 2 during the shuanghe fm sedimentation the paleoelevation was between 0 9 0 7 0 7 km asl and 2 9 0 6 km asl 18omw 9 5 1 1 2 our results suggest that a stepwise uplift of jianchuan basin and crustal thickening initiated during the eocene was the cause of passive surface uplift of the southeastern tibetan plateau tp rather than miocene lower crustal flow

refinement of eocene lapse rates fossil leaf altimetry and north american cordilleran surface elevation estimates abstract estimates of continental paleoelevation using proxy methods are essential for understanding the geodynamic climatic and geomorphoric evolution of ancient orogens fossil leaf paleoaltimetry one of the few quantitative proxy approaches uses fossil leaf traits to quantify differences in temperature or moist enthalpy between coeval coastal and inland sites along latitudes these environmental differences are converted to elevation differences using their rates of change with elevation lapse rate here we evaluate the uncertainty associated with this method using the eocene north american cordillera as a case study to do so we develop a series of paleoclimate simulations for the early 55 49 ma and middle eocene 49 40 ma period using a range of elevation scenarios for the western north american cordillera simulated eocene lapse rates over western north america are 5 c km and 9 8 kj km close to moist adiabatic rates but significantly different from modern rates further using linear lapse rates underestimates high altitude 3 km temperature variability and loss of moist enthalpy induced by non linear circulation changes in response to increasing surface elevation ignoring these changes leads to kilometer scale biases in elevation estimates in addition to these biases we demonstrate that previous elevation estimates of the western cordillera are affected by local climate variability at coastal fossil leaf sites of up to 8 c in temperature and 20 kj in moist enthalpy a factor which further contributes to elevation overestimates of 1 km for early eocene floras located in the laramide foreland basins and underestimates of 1 km for late middle eocene floras in the southern cordillera we suggest a new approach for estimating past elevations by comparing proxy reconstructions directly with simulated distributions of temperature and moist enthalpy under a range of elevation scenarios using this method we estimate mean elevations for the north american cordillera of 2 km using proxy temperatures and 3 km using proxy moist enthalpy this discrepancy is likely related to an inconsistency between the proxy data for temperature and moist enthalpy the combination of temperature and moist enthalpy estimates implies a warm and dry environment which is inconsistent with geological evidence for humid conditions our study emphasizes that lapse rates in warm climate were likely much different than today s and highlights the advantages of using climate models to understand past climate states and regional circulation patterns to derive more accurate paleoelevation estimates using proxy temperature and moist enthalpy

advance retreat and halt of abrupt gravel sand transitions in alluvial rivers downstream fining of bed sediment in alluvial rivers is usually gradual but often an abrupt decrease in characteristic grain size occurs from about 10 to 1 mm i e a gravel sand transition gst or gravel front here we present an analytical model of gst migration that explicitly accounts for gravel and sand transport and deposition in the gravel reach sea level change subsidence and delta progradation the model shows that even a limited gravel supply to a sand bed reach induces progradation of a gravel wedge and predicts the circumstances required for the gravel front to advance retreat and halt predicted modern gst migration rates agree well with measured data at allt dubhaig and the fraser river and the model qualitatively captures the behavior of other documented gravel fronts the analysis shows that sea level change subsidence and delta progradation have a significant impact on the gst position in lowland rivers

tectonic significance of paleobotanically estimated climate and altitude of the late eocene erosion surface colorado erosion beveled the laramide front range uplift in colorado to a surface of low relief by the end of the eocene this study uses j a wolfe s new multivariate climate analysis techniques to determine the paleoelevation of this regional surface by examining the overlying 35 ma florissant flora a multiple regression model explaining 93 3 of the variance in mean annual temperature was developed using wolfe s dataset of 31 leaf physiognomic character states for 86 modern vegetation sites these character states were scored on 29 species collected from one facies of the florissant lake beds the paleotemperature estimate of mean annual temperature 10 7 plus minus 1 5c derived from these data when combined with sea level temperature and terrestrial lapse rate implies a late eocene paleoelevation of 2 4 2 7 km pliocene uplift is thus not required to explain the present elevation of 2 5 km it is unclear when and why the southern rocky mountains achieved this elevation magmatic crustal thickening can explain the late eocene high elevation of the southern rockies but neither this mechanism nor compressive thickening explains why the great plains which are tied to the florissant elevation by the wall mountain tuff were also high this paleoelevation estimate indicates that regional surfacesmore of planation could be formed at high elevation in the eocene probably because of peculiarities of the eocene climate less

palynological evidence for the latest oligocene early miocene paleoelevation estimate in the lunpola basin central tibet uplift of the tibetan plateau is ultimately driven by the cenozoic collision between the indian and eurasian plates and their continued convergence one approach for studying the tibetan plateau uplift is to verify the paleoelevation changes from collision to present day this is important for understanding both the tectonics and the climatic effects the new high resolution palynological record of the uppermost oligocene to the lowest miocene strata from the lunpola basin indicates that the vegetation types during the latest oligocene earliest miocene were dominated by mixed coniferous broadleaved forests being different from the modern steppe vegetation by using the coexistence approach to the fossil pollen records after calibration the effects of temperature difference and the lapse rate a maximum paleoelevation of 3190 100 m asl was estimated in the lunpola basin in the latest oligocene earliest miocene being 1500 to 2000 m lower compared with the previous oxygen isotope paleoelevation in the same region

investigations of continuous bed load saltating process particle saltating motions during bed load transport are dominated by the forces acting upon particles and the random process of the particles impacting on and rebounding from the channel bed a real time flow visualization technique is developed in this study to measure particle saltating trajectories corresponding velocities and impacting and rebounding angles based on the experimental data regression equations for the dimensionless saltating length height and velocity were obtained a numerical model that is able to simulate the continuous saltating process of a single particle was developed the model was calibrated and verified with the experimental data and the results were satisfactory the model was also used to generate a series of synthetic data based on these data and the flume data collected by previous investigators a bed load equation was derived

terrestrial cosmogenic nuclides as paleoaltimetric proxies the production rates of terrestrial in situ cosmogenic nuclides depend on the altitude and can therefore be used to constrain paleoaltitudes if the history of cosmogenic nuclide production in a region can be constrained this chapter discusses the theory behind cosmogenic nuclide paleoaltimetry sampling strategies and practical limitations of the technique three exposure scenarios may allow for the calculation of past altitudes 1 exposure for a finite time period at a single elevation and without erosion or burial followed by immediate shielding from further production of cosmogenic nuclides 2 steady uplift of a surface throughout nuclide production without erosion or burial and 3 exposure of a sample without erosion or burial for a sufficient duration that the concentration of a cosmogenic radionuclide has reached equilibrium to constrain paleoelevation all exposure scenarios require independent evidence of the depth history of a sample during exposure to cosmic rays because production rates attenuate rapidly in rock depth profiles and measuring multiple nuclides allow for better constraints of parameters in paleoaltitude calculations

palaeoaltimetry from energy conservation principles a knowledge of past changes in the mean elevations of large continental areas is important for understanding both dynamic processes in the earth s mantle 1 and the evolution of the global climate 2 but virtually all methods for determining palaeoelevations are problematic in part because changes in either elevation or climate can give rise to the same observed geological phenomena 4 ideally palaeoelevations would be inferred directly from estimates of palaeopressure and it has recently been shown 5 that vesicles in basaltic lava flows preserve a record of atmospheric pressure at the altitude of emplacement however the elevations thus obtained have large errors 1 4 km and the method can at present be applied only to lavas that have had a simple emplacement history 5 palaeobotanical methods for estimating palaeoelevation have received much attention 6 12 but they rely on empirical temperature elevation relationships the uncertainties in which are difficult to evaluate for past climates here we describe an alternative palaeobotanical approach based on energy conservation in the atmosphere in which fossil leaf assemblages are used to infer enthalpy rather than temperature this approach is relatively insensitive to palaeoclimate with an expected error in palaeoelevation of 700 m

biomarker reconstruction of the early eocene paleotopography and paleoclimate of the northern sierra nevada we reconstruct ancient temperature and elevation gradients across the early eocene 52 49 ma northern sierra nevada california united states using organic molecular proxies that record atmospheric and ground level effects of topography paleoelevation was determined by reconstructing the change in the hydrogen isotopic composition of precipitation d precip and mean annual temperature t gdgt glycerol dialkyl glycerol tetraethers from the isotopic composition of fossil angiosperm leaf n alkanes and the distribution of microbially produced soil tetraethers preserved in leaf bearing sediments organic molecular data produce equivalent range scale d n alkane and channel t gdgt paleoelevation estimates that show the northern sierra nevada was a warm 6 8 c warmer than modern high elevation 2 km and moderate to low relief landscape at the eocene climatic optimum modern northern sierra nevada topography likely refl ects post paleocene reduction of mean surface elevation and late cenozoic increases in relief

tracking of saltating sand trajectories over a flat surface embedded in an atmospheric boundary layer abstract saltation is a major mechanism for the transport of soil particles in the present study we carried out wind tunnel tests to examine the saltating trajectories of two types of natural sand collected from a beach diameter d 300 500 m and 200 300 m respectively as well as sand from the taklimakan desert d 100 125 m in an atmospheric boundary layer consecutive images of saltating particles were recorded using a high speed digital camera at a rate of 2000 fps with a spatial resolution of 1024 1024 pixels the high temporal resolution of the acquired images enabled us to study the particle motion very close to the surface the saltating particle trajectories were reconstructed from consecutive images and the physical quantities characterizing the initial and final stages of the particle flight in the windward direction at friction velocities of about 10 25 above the threshold friction velocity u u t 1 11 1 26 were analyzed statistically in addition the transverse deviation of the saltating particles from the main streamwise direction was evaluated the results shed new light on the complicated motions involved in sand saltation and should prove useful in the evaluation and formulation of theoretical models

deconvolution technique to separate signal from noise in gravel bedload velocity data a deconvolution procedure is presented to estimate the probability density function of bedload transport velocity from noisy stationary data collected using the bottom tracking feature of acoustic doppler current profilers adcps the procedure involves the optimization of a computational summation of random variables for the instrument noise assumed to be gaussian with zero mean and the spatially averaged bedload velocity within the insonified area of each acoustic beam v the procedure was tested on two adcp time series measured in two different gravel bed rivers fraser river and norrish creek models generated using either a semitheoretical compound poisson gamma distribution or an empirical gamma distribution for v were similar and did not differ significantly from the distribution of the original data optimized distributions for v were highly positively skewed the instrument noise was comparable to instrument noise for adcp water velocity measurements i e an order of magnitude greater t

morphodynamics of an extended bar complex fraser river british columbia we investigate large scale morphologic changes over a 65 year period in a major sedimentation zone within the 50 km long wandering gravel bed reach of lower fraser river british columbia this reach remains in a relatively pristine state compared with many major rivers in populated regions even though various forms of human interference have occurred over the past century to mitigate flooding and erosion concerns a template of channel evolutionary development is identified consisting of extended periods of orderly accretion of unit bars by deposition of gravel sheets controlled by the major riffles in the river when this process constricts channel conveyance an avulsion occurs and the major bar complexes are reorganized the recognition of fairly predictable short term behavior can potentially aid the development of models of sediment transport and channel evolution accordingly results of the detailed descriptive analysis are compared with a gis based probabilistic approach developed from transition state analysis this reveals that the river has a far stronger tendency to retain its existing morphology than to change its form within a roughly decennial time scale regardless of the magnitude of intervening flows but that this tendency gradually declines over time as major bar and island complexes are re worked by sediment exchange the timescale for major bar development appears to be of the order 30 years while complete sediment exchange occurs within a century copyright 2012 john wiley sons ltd

morphology and controls on the position of a gravel sand transition fraser river british columbia alluvial river channels often exhibit a relatively abrupt transition from gravel to sand bedded conditions the phenomenon is well documented but few prior studies have analyzed the spatial variability through reaches where transitions occur the downstream fining pattern observed in the fraser river is cited as a classic example of an abrupt gravel sand transition in a large alluvial channel however important questions regarding the exact location of the transition its sedimentology and morphology and what controls its location remain unanswered here we present observations of the downstream change in bed material grain size river bed topography and channel hydraulics through the reach within which the transition occurs these observations indicate that the gravel sand transition is characterized by a terminating gravel wedge but there are patches of gravel downstream of the wedge forming a diffuse extension we show that there is a dramatic decrease in shear stress at the downstream end of the wedge and a consequent cessation of general gravel mobility we argue that the patches of gravel observed beyond the wedge are the result of enhanced mobility of fine gravel over a sand bed we also find that sand in suspension declines rapidly at the downstream end of the wedge suggesting that sand is delivered to the bed completing the sedimentary conditions for a gravel sand transition we propose that the break in river slope associated with the transition is a consequential feature of the transition

sediment transport along lower fraser river 1 measurements and hydraulic computations a comprehensive program of sediment transport measurements was conducted along lower fraser river british columbia between 1966 and 1986 the data yield a detailed sediment budget annual total suspended loads at three stations are virtually identical averaging 17 106 tonnes year t yr 1 the suspended sand load is about 5 5 106 t yr 1 about one third of the total in the gravel bed reach of the river the sand behaves as wash load significant transport of gravel begins at agassiz at a discharge of about 5000 m3 s 1 the annual gravel transport was estimated to be about 0 23 106 t yr 1 only 1 of the total load all of this material is deposited in the reach upstream of mission at mission sands finer than 0 177 mm make up more than 50 of the suspended sand load but are virtually absent from the sand bed therefore a portion of the sand load at mission is wash load the total bed material load here was estimated to be 3 0 106 t yr 1 about 18 of the total sediment load virtually all of the bed material load was transported in intermittent suspension near the bed less than 5 occurring as bed load in the long term the suspended sand load upstream is approximately equal to the total sand load at mission however within individual years some of the sand is stored within the reach temporarily and then reentrained later

the partitioning of the total sediment load of a river into suspended load and bedload a review of empirical data the partitioning of the total sediment load of a river into suspended load and bedload is an important problem in fluvial geomorphology sedimentation engineering and sedimentology bedload transport rates are notoriously hard to measure and at many sites only suspended load data are available often the bedload fraction is estimated with rule of thumb methods such as maddock s table which are inadequately field tested here the partitioning of sediment load for the pitzbach is discussed an austrian mountain stream for which high temporal resolution data on both bedload and suspended load are available the available data show large scatter on all scales the fraction of the total load transported in suspension may vary between zero and one at the pitzbach while its average decreases with rising discharge i e bedload transport is more important during floods existing data on short and long term partitioning is reviewed and an empirical equation to estimate bedload transport rates from measured suspended load transport rates is suggested the partitioning averaged over a flood can vary strongly from event to event similar variations may occur in the year to year averages using published simultaneous short term field measurements of bedload and suspended load transport rates maddock s table is reviewed and updated long term average partitioning could be a function of the catchment geology the fraction of the catchment covered by glaciers and the extent of forest but the available data are insufficient to draw final conclusions at a given drainage area scatter is large but the data show a minimal fraction of sediment transported in suspended load which increases with increasing drainage area and with decreasing rock strength for gravel bed rivers whereby in large catchments the bedload fraction is insignificant at 1 for sand bed rivers the bedload fraction may be substantial 30 50 even for large catchments however available data are scarce and of varying quality long term partitioning varies widely among catchments and the available data are currently not sufficient to effectively discriminate control parameters

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

depositional setting fossil flora and paleoenvironment of the early eocene falkland site okanagan highlands british columbia the fossil flora and depositional setting of the early eocene falkland site in the southern interior of british columbia canada is reported in detail for the first time using a census sampling approach the falkland site is part of the series of okanagan highlands fossil localities in british columbia and washington state that represent relatively cool upland environments within the context of the greenhouse world of the early eocene providing microthermal mean annual temperature mat 13 c climatic conditions for the establishment of cool adapted plants geographically adjacent to subtropical elements from lowland floras plant community composition of the falkland flora is most similar to the republic washington and mcabee british columbia floras based on high sorenson similarity coefficients together forming a southern cluster of okanagan highlands sites the site is a lacustrine deposit that formed in a volcanically active landscape paleoclimate reconstructions based on leaf physiognomy

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

revisiting the linear theory of sand dune formation a linear stability theory for dune and antidune formation is presented that implements a rotational two dimensional flow model as in previous linear theories the phase lag between sediment transport and bed elevation remains the main mechanism driving instability however it is shown that this phase lag varies significantly in a neighbourhood of the bed moreover since the layer in which sediments are moving has a finite though small thickness it is assumed that the perturbations of the fluid stress driving bedload transport should be evaluated at the top of the layer itself it is shown that such an apparently minor modification of the classical approach alters remarkably the balance between stabilizing and destabilizing effects that drives the instability process this also allows a clarification of the debated role of bedslope on the formation of dunes and antidunes following the above ideas antidunes are shown to form in the absence of suspended sediment load and without any effect associated with sediment inertia the present analysis ultimately allows a successful unification of the theories of dune and antidune formation

a review of paleotemperature lapse rate methods for estimating paleoelevation from fossil floras one widely applied method for estimating paleoelevation from fossil floras uses the relation between vegetation and temperature to estimate mean annual temperature from two isochronous fossil assemblages one at elevation and one at or near sea level and the difference between these temperatures is multiplied by the reciprocal of a temperature lapse rate to estimate paleoelevation three fundamentally different approaches have been developed and these vary both in the method by which paleotemperatures are estimated and in the way by which modern lapse rates can be measured paleotemperature methodologies include the use of plant physiognomy or the use of nearest living relatives lapse rate methodologies use either a global terrestrial lapse rate as the world mean a regional terrestrial lapse rate that represents a large portion of a continent or a local terrestrial lapse rate for areas narrowly confined by latitude and longitude other variables and or corrective factors that should be considered in these applications include the thermal effects of continentality and elevated land surfaces in the continental interior and standardization to compensate for fluctuations or variability in sea level global climate change and paleolatitude these different methodologies can be contrasted by their common application to the late eocene florissant flora of colorado with results ranging from 455 to 4133 meters

bed and flow dynamics leading to sediment wave initiation 1 new piv based experiments show that the nascent seed waves from which both ripples and dunes develop are generated on planar mobile sediment beds in a two stage process the first stage comprises the motion of random sediment patches that reflect the passage of sediment transport events caused by attached eddies these eddy transport events propagate at speeds that are proportional to their size and less than overhead eddy convection velocities but potentially larger than local average fluid and sediment velocities in the second stage interactions of the moving patches result in a bed disturbance that exceeds a critical height and interrupts the bed load layer quasi regular seed waves are then generated successively downstream of this stabilised growing disturbance via a scour deposition wave that arises from the requirement of sediment mass conservation and the sediment transport and bed stress distributions downstream of a bed perturbation seed waves are thereby of preferred lengths that scale with the grain size i e length o 130 grain diameters agreeing with compiled measurements this two stage generation mechanism is valid for fully turbulent hydraulically smooth and rough bed flows of small to large sediment transport rates it is furthermore valid for laminar flows although the critical disturbances leading to seed wave generation arise through bed discontinuities and not eddy based sediment transport events the identified generation mechanism which accounts for turbulence effects explains the observed similar scaling of alluvial closed conduit and lightweight sediment seed waves the present measurements highlight further aspects of the flow dynamics preceding seed wave generation including decreases in von karman s constant due to bed mobility near bed eddy convection speeds in excess of local double averaged in time and space streamwise velocities and the validity of the four range spectral scaling model for open channel flows proposed earlier by nikora

form and growth of bars in a wandering gravel bed river the changing form of developing alluvial river bars has rarely been studied in the field especially in the context of the fixed compound mainly alternate gravel bars that are the major morphological feature of the wandering style century scale patterns of three dimensional growth and development and the consequent scaling relations of such bars are examined along the gravel bed reach of lower fraser river british columbia canada a retrospective view based on maps and aerial photographs obtained through the twentieth century shows that individual bars have a life history of about 100 years except in certain protected positions a newly formed gravel bar quickly assumes its ultimate thickness and relatively quickly approaches its equilibrium length growth continues mainly by lateral accretion of unit bars consistent with the lateral style of instability of the river bar growth is therefore allometric mature bars approach equilibrium dimensions and volume that scale with the overall size of the channel accordingly the bars conform with several published criteria for the ultimate dimensions of alternate barforms sand bars observed farther downstream have notably different morphology fraser river presents a typical wandering channel planform exhibiting elements of both meandered and low order braided channels hydraulic criteria to which the fraser bars conform illustrate why this planform develops and persists the modest rate of bed material transfer along the channel typical of the wandering type determines a century length time scale for bar development this time scale is consistent with estimates that have been made for change of the macroform elements that determine the overall geometry of alluvial channels copyright 2009 john wiley sons ltd

flow and sediment suspension events over low angle dunes fraser estuary canada 1 the morphodynamics of large sand bedded rivers and estuaries are ultimately controlled by the way bed material is moved and the development of large subaqueous sand dunes that control hydraulic flow resistance it is widely thought that the primary mechanism for moving sandy bed material in these channels is large scale coherent flow structures that cause suspension events whose properties vary with flow especially in tidally influenced environments here we examine mean flow and sediment suspension events over low angle dunes lee face angle 30 in the unsteady flow of the fraser estuary canada at high tide flow nearly ceased and a salt wedge entered the channel forcing salt water under the downstream moving fresh water the salt wedge persisted in the channel until late in the falling tide causing stratification in the water column and instabilities along the saline fresh water interface at low tide mean velocities peaked and forced the saline water out of the channel flow over the low angle dunes displayed topographically induced patterns previously observed over high angle dunes but permanent flow separation was not observed large scale sediment suspension events dominated sediment flux during low tide and became larger scale yet less frequent as the tide began to rise the suspension events appeared to form over the lower stoss of the dunes and grew up over the bed forms and less commonly emerged downstream of the crest suspension events move 69 of the total sediment in the flow above low angle dunes when they are present

evaluation of the saltation process of bed materials by video imaging under altered bed roughness the purpose of this paper is to examine the nature of particle saltation and movement over the beds of fixed roughness from flume experiments a series of experiments are carried out to study the saltation of individual sand particles of different sizes over rough beds under different flow conditions a 3 d acoustic doppler velocimeter is used to record the fluid velocity components subsequently under different flow conditions the images of released sand particles are recorded using high speed video imaging technique systematic analysis is made with regard to the forces acting on the grains and the variation of their magnitudes along the saltation trajectories of the grains relations between the saltation parameters flow intensity and bed roughness are developed the distributions of the angle of orientations during a single saltation follows almost a gaussian distribution the shape of the gaussian distribution depends on the particle size and bed roughness particle collisions with rough beds and the resulting coefficients of restitution are also discussed a theoretical framework is developed to compute the mean particle velocity considering the spin in the energy balance equation results of the detailed analysis using the imaging technique are much better than in previously reported studies copyright 2013 john wiley sons ltd

stable width and depth of straight gravel rivers with heterogeneous bed materials mathematical model for defining stable width and depth of straight gravel rivers is presented in which it is revealed that the major agency for maintaining stable channel is lateral diffusion of longitudinal fluid momentum due to turbulence the primary quantities which determine the stable channel geometry are found to be flow discharge longitudinal free surface slope the median size of bed material and gradation of the bed material increasing gradation is found to increase the depth and decrease the width introduction of one loose and the other rigid bank in laboratory experiments provides good examples to test the model in which four kinds of sand were used to test the gradation effect these laboratory data support the mathematical model presented herein the theory also performs well when it is applied to natural gravel rivers

improving sediment load estimations the case of the yarlung zangbo river the upper brahmaputra tibet plateau abstract suspended sediment load of a river represents integrated results of soil erosion landform change and ecosystem variation occurring within the river basin accurate estimation of suspended sediment load is helpful for distinguishing the impact of natural and anthropogenic factors on earth system processes within river basin under global climate change suspended sediment load with long term in situ observation limited by harsh conditions can be estimated by sediment rating curves and various subdivision methods with suspended sediment concentration and discharge data of low frequency new sediment rating curve subdivision methods based on flood ranks and suspended sediment concentration stages were proposed in this study the flood ranks subdivision method which defined a flood to begin when discharge exceeded the critical discharge value rank1 or the previous peak flow rank2 and the later and end when fluctuating discharge reached the peak flow of current flood again which is the beginning of next flood or lowered to the critical discharge value the last rank was suitable for application in the basin where sediments were mainly transported and exhausted in early events the suspended sediment concentration stages subdivision method i e the rising and falling limbs of suspended sediment concentration separated by peak dates estimated based on accumulated precipitation was suitable for application in the basin where soil erosion was closely related to precipitation compared to the traditional sediment rating curve and seasonal discharge classes and discharge stages subdivision methods these newly proposed methods can improve suspended sediment concentration and subsequently suspended sediment load estimation in the middle reach of the yarlung zangbo river with higher coefficients of determination and nash sutcliffe efficiency coefficients and lower bias and root mean square errors moreover combination of the two separately developed methods presented further improved estimation the newly proposed sediment rating curve subdivision methods could be helpful for suspended sediment load estimation and therefore are useful for water resource management within river basins

palaeobotanical evidence for a warm cretaceous arctic ocean the cretaceous period was a time of global warmth1 4 mid cretaceous equatorial temperatures were similar to today s5 but the equator to pole temperature gradient is the subject of some controversy5 7 although it is unlikely that the poles were ice free8 10 fossil evidence3 5 11 12 indicates that near polar temperatures were much higher than they are today little is known moreover about oceanic poleward heat transport and this makes it hard to model the cretaceous climate or to evaluate the extent to which it provides an analogue for a greenhouse world warmed by increased atmospheric co2 alone here we use relationships between leaf physiognomy such as shape and size and modern climate to determine cretaceous climate conditions in the arctic region from fossil leaves we find that the arctic ocean was relatively warm remaining above 0 c even during the winter months this implies that there was significant poleward heat transport during all seasons

regional clastic sediment yield in british columbia the data archive of the water survey of canada supplemented by data of the british columbia hydro and power authority is used to investigate the areal pattern of fluvial sediment yield in british columbia the data represent suspended sediment loads at 63 stations derived from observations within the period 1966 1985 in most of the province there is a single annual peak in sediment transport in spring corresponding to the dominant snowmelt freshet however on the coast winter rainfall induces the sediment peak and in the coast and cascade mountains there is a transitional regime with two peaks from 65 to 90 of annual sediment yield occurs in the spring three months sediment yield per unit area specific sediment yield increases with drainage area at all scales from 10 up to 30 000 km2 the pattern persists seasonally throughout the year this contradicts the conventional model in which sediment yield declines downstream because of deposition along channels of a portion of the load derived from e

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

threshold for particle entrainment into suspension laboratory observations regarding the limit conditions for particle entrainment into suspension are presented a high speed video system was used to investigate conditions for the entrainment of sediment particles and glass beads lying over a smooth boundary as well as over a rough bed the results extend experimental conditions of previous studies towards finer particle sizes a criterion for the limit of entrainment into suspension is proposed which is a function of the ratio between the flow shear velocity and particle settling velocity observations indicate that particles totally immersed within the viscous sublayer can be entrained into suspension by the flow which contradicts the conclusions of previous researchers a theoretical analysis of the entrainment process within the viscous sublayer based on force balance considerations is used to show that this phenomenon is related to turbulent flow events of high instantaneous values of the reynolds stress in agreement with previous observations in the case of experiments with a rough bed a hiding effect was observed which tends to preclude the entrainment of particles finer than the roughness elements this implies that as the ratio between particle and roughness element sizes becomes smaller progressively higher bed shear stresses are required to entrain particles into suspension on the other hand an overexposure effect was also observed which indicates that a particle moving on a smooth bed is more prone to be entrained than the same particle moving on a bed formed by identical particles

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

middle miocene paleoaltimetry of southern tibet implications for the role of mantle thickening and delamination in the himalayan orogen the stable isotope composition of pedogenic and early diagenetic carbonates from the oiyug basin of southern tibet allows model estimates of the paleoaltimetry of the tibetan plateau for the middle miocene pedogenic calcium carbonate nodules have average d 18 occ values of 219 6 whereas nodular lacustrine dolomites range in composition from 27 6 to 25 5 the most negative of the carbonate isotope values can be used to constrain the oxygen isotope composition of paleoprecipitation from which model estimates of paleoaltimetry can be made model results indicate that the southern tibetan plateau achieved elevations of 5200 11370 2605 m by at least 15 ma our results are identical within uncertainty to previous workers paleoelevation estimates based on oiyug basin fossil floral physiognomy this is the first time that two paleoaltimeters have been directly compared and are in accord collectively these data strongly support tectonic models in which thickening of mantle lithosphere beneath the domain of crustal thickening and subsequent detachment of the mantle lithosphere plays an indiscernible role in the elevation history of this part of the himalaya tibet orogenic system

factors controlling specific sediment yield in the upper indus river basin northern pakistan estimates of sediment yield are essential in water resources analysis modelling and engineering in investigations of continental denudation rates and in studies of drainage basin response to changes in climate and land use the availability of high resolution global environmental datasets offers an opportunity to examine the relationships between specific sediment yield sysp and drainage basin attributes in a geographical information system gis environment this study examines sysp at 14 long term gauging stations within the upper indus river basin twenty nine environmental variables were derived from global datasets the majority with a 1 1 km resolution the sysp ranges from 194 to 1302 t km 2 yr 1 for sub basins ranging from 567 to 212 447 km2 the high degree of scatter in sysp is greatly reduced when the stations are divided into three groups upper glacierized sub basins lower monsoon sub basins and the main indus river percentage snow ice cover lcs emerges as the single major land cover control for sysp in the high mountainous upper indus river basin a regression model with percentage snow ice cover lcs as the single independent variable explains 73 4 of the variance in sysp for the whole indus basin a combination of percentage snow ice cover lcs relief and climate variables explains 98 5 of the variance for the upper glacierized sub basins for the lower monsoon region a regression model with only mean annual precipitation p explains 99 4 of the variance along the main indus river a regression model including just basin relief r explains 92 4 of the variance in sysp based on the r2adj and p value statistics the variables used are capable of explaining the majority of variance in the upper indus river basin copyright 2007 john wiley sons ltd

tertiary climatic changes at middle latitudes of western north america abstract a new multivariate analysis of leaf physiognomy provides the basis for estimating various climatic parameters for angiosperm leaf assemblages estimates from this climate leaf analysis multivariate program clamp are both accurate valid and precise repeatable application of clamp to fossil leaf assemblages from western north america confirms that eocene mean annual temperature mat was generally high early eocene mat 19 c at paleolat 70 n and 27 c at paleolat 45 n significant fluctuations 5 8 in mat occurred during the eocene each successive warm period was cooler than the preceding warm period mean annual range of temperature mart was generally low during the eocene especially at middle latitudes but then markedly increased by 12 13 c at 33 ma as mat decreased by 7 8 c these changes at 33 ma largely involved a decrease in cold month mean temperature which continued to decline into the early miocene but then increased significantly into the mid miocene thermal optimum warm month mean temperature changed little from the eocene through the early miocene this parameter however markedly decreased at 13 ma which coincides with the growth of the east antarctic ice sheet clamp also indicates that the coastal region of western north america had significantly higher mat than interior regions such as the great basin and rocky mountains these differences in mat appeared by or during the eocene and indicate that much of the interior had high altitudes in the paleogene these inferences have a significant bearing on global circulation models proposed for tertiary climates

temporal variations in lake water temperature paleoenvironmental implications of lake carbonate δ18o and temperature records abstract 18 o and clumped isotope measurements of lacustrine carbonates provide important records of past terrestrial climate and paleoelevation however one of the primary challenges interpreting these data is constraining the relationship between mineral formation temperature and seasonal and mean annual climate we examined surface water temperature records from 88 lakes across the globe to develop transfer functions that relate seasonal water surface temperature to mean annual air temperature these transfer functions provide a means of reconciling proxy measures of water temperature with annual climatic conditions mean annual surface water temperature is related to mean annual air temperature maat 0 0318 t water 2 2 195 t water 12 607 r 2 0 96 independent of lake size with consistently higher mean water temperatures than air n hemisphere spring april june mean lake surface temperatures maat 0 0097 t water 2 1 379 t water 8 227 r 2 0 94 are only slightly warmer than maat for lakes in all climate zones while summer water temperatures jja maat 0 0055 t water 2 1 476 t water 18 915 r 2 0 90 may be 10 20 c warmer than maat for cold climate lakes comparison of carbonate stable isotopic data from sites with different timescales of carbonate formation such as found along latitude or elevation gradients can lead to large over or underestimates of past temperature accurate paleoclimatic interpretation of isotopic proxies or use of temperature proxy constraints i e fossil leaves to estimate lake temperature and calculate water 18 o thus requires appropriate application of water temperature air temperature transfer functions particularly when considering ancient cool high elevation lake systems

a critical perspective on 1 d modeling of river processes gravel load and aggradation in lower fraser river 1 we investigate how well a width averaged morphodynamic model can simulate gravel transport and aggradation along a highly irregular 38 km reach of lower fraser river and discuss critical issues in this type of modeling bed load equations with plausible parameter values predict a gravel input consistent with direct measurements and a sediment budget simulations using spatially varying channel width and forced by dominant discharge or a 20 year hydrograph match the observed downstream fining well they reproduce major qualitative features of a 47 year sediment budget and match maximum local rates of aggradation and degradation to well within a factor of 2 locations and rates of aggradation and degradation are influenced by channel constrictions runs for single years of unusually high or low peak discharge suggest that the main transfers of gravel occur in different parts of the reach in different years one dimensional morphodynamic modeling of highly nonuniform rivers has serious conceptual limitations but may be a valuable complement to empirical approaches

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

partial transport of a sand gravel sediment grains of a single size within a mixed size bed are entrained over a range of flows within this range some grains exposed on the bed surface are active entrained at least once over the duration of a transport event while the remaining surface grains are immobile a condition we define as partial transport we demonstrate the existence and domain of partial transport using observations of grain entrainment on time series of bed photographs of flume experiments with a widely sorted sand gravel mixture the active proportion of the bed surface increases with bed shear stress 0 at a given 0 90 of the active grains are entrained when the cumulative mass transported exceeds approximately 4 times the active mass on the bed mobilization of grains in a size fraction increases from 10 to 90 over a range of 0 of a factor of 2 the bounds of this range increase with grain size di so that at a given 0 sizes over a range of a factor of 4 are in a state of partial transport fractional transport rates are independent of di for fully mobilized fractions and decrease rapidly with di for partially mobile fractions partial transport is associated with substantial transport rates of finer fully mobile sizes limits both the rate and size distribution of grain exchange with the bed subsurface and may be the dominant transport condition in many gravel bed rivers

estimating bedload transport in a large sand gravel bed river from direct sampling dune tracking and empirical formulas three methods used to estimate river bedload discharges were compared in a large sand gravel bed river the unit and total bedload transport rates estimated by sediment sampling dune tracking method and the equations of van rijn and meyer peter and muller were compared the analysis was based on a large data set obtained from field surveys that combined sediment sampling acoustic doppler profiler adp measurements and multibeam echosoundings of the middle reach of the river loire france for contrasting flow conditions ranging from low flows to 2 year floods for transport stages between 2 and 6 i e between the annual mean discharge and the discharge for a 2 year flood the tested equations predicted fairly well the unit and total bedload discharges and roughly estimated the temporal variability of the bedload during floods for these transport conditions the best agreement with the sediment sampling measurements was observed with the van rijn formula for lower flow conditions the tested formulas provide lower estimates than those sampled to improve the accuracy of the equations for low flows potential solutions include integrating near bed turbulences and non uniformity of bed particles into the models the ability of the formulas to predict the temporal variability of the bedload can be improved by using the bedform roughness to adjust the estimates the bedload transport rates calculated with dune tracking method are lower than the fluxes sampled because a substantial fraction of the bedload does not participate to the dune migration finally a first rating curve that was implemented for the river loire estimates the annual bedload discharge for 2010 to be 480 000 t

periodic saltation over hydrodynamically rough beds aeolian to aquatic we determine approximate analytical solutions for average periodic trajectories of particles that are accelerated by the turbulent shearing of a fluid between collisions with a hydrodynamically rough bed we indicate how the viscosity of the fluid may influence the collisions with the bed the approximate solutions compare well with periodic solutions for average periodic trajectories over rigid bumpy and erodible beds that are generated numerically the analytic solutions permit the determination of the relations between the particle flux and the strength of the shearing flow over a range of particle and fluid properties that vary between those for sand in air and sand in water

surface based fractional transport rates mobilization thresholds and partial transport of a sand gravel sediment twenty eight coupled observations of flow transport and bed surface grain size distribution were made in a laboratory flume using a wide range of flows and a sediment with a very poorly sorted bimodal grain size distribution these observations permit the transport rates of individual size fractions to be scaled by the proportion of each size immediately available for transport on the bed surface the key to our observations is the use of a sediment in which each size fraction has been painted a different color which permits reliable repeatable and nondestructive measurement of the bed surface grain size distribution from photographs of the bed surface at a given flow the fractional transport rates may be divided into two parts a finer grained portion within which fractional transport rates are a function only of their proportion on the bed surface and total transport rate and a coarser grained portion for which fractional transport rates also depend on the proportion of individual grains within a fraction that remain essentially immobile throughout the experimental run we define the latter condition as one of partial transport and observe that the grain size separating partial and fully mobilized transport consistently increases with flow strength complete mobilization of a size fraction occurs at roughly twice the shear stress necessary for incipient motion of that fraction zones of partial and full mobility are quite distinct when fractional transport rates are scaled by the bed surface grain size distribution although a region of partial transport is evident when these data and other experimental and field observations are scaled by the bulk grain size distribution of the sediment bed critical shear stresses for the incipient motion of individual fractions in our experimental sediment vary over an order of magnitude a result strongly in contrast to many earlier observations but consistent with our observations of incipient motion in sediments with bimodal grain size distributions

temporal variations in bedload transport rates associated with the migration of bedforms temporal variations in bedload transport rates that occur at a variety of timescales even under steady flow conditions are accepted as an inherent component of the bedload transport process rarely however has the cause of such variations been explained clearly we consider three data sets obtained from laboratory experiments that refer to measurements of bedload transport made with continuously recording bedload traps each data set is characterized by a predominant low frequency oscillation on which additional higher frequency oscillations generally are superimposed the period of these oscillations as isolated through the use of spectral analysts ranged between 0 47 and 168 minutes and was associated unequivocally with the migration of bedforms such as ripples dunes and bars the extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time with respect to the period of a given bedform several theoretical probability distribution functions have been developed to describe the frequency distributions of relative bedload transport rates that are associated with the migration of bedforms einstein 1937b hamamori 1962 carey and hubbell 1986 these distribution functions were derived without reference to a sampling interval we present a modification of hamamori s 1962 probability distribution function generated by monte carlo simulation which permits one to specify the sampling interval in relation to the length of a bedform comparisons between the simulated and observed frequency distributions that were undertaken on the basis of the data described herein are good significant at the 90 per cent confidence level finally the implications that temporal variability which is associated with the migration of bedforms have for the accurate determination of bedload transport rates are considered

sensitivity of a hydraulic model to channel erosion uncertainty during extreme flooding recent research into flood modelling has primarily concentrated on the simulation of inundation flow without considering the influences of channel morphology river channels are often represented by a simplified geometry that is implicitly assumed to remain unchanged during flood simulations however field evidence demonstrates that significant morphological changes can occur during floods to mobilize the boundary sediments despite this the effect of channel morphology on model results has been largely unexplored to address this issue the impact of channel cross section geometry and channel long profile variability on flood dynamics is examined using an ensemble of a 1d 2d hydraulic model lisflood fp of the 1 2000 year recurrence interval floods in cockermouth uk within an uncertainty framework a series of simulated scenarios of channel erosional changes were constructed on the basis of a simple velocity based model of critical entrainment a monte carlo simulation framework was used to quantify the effects of this channel morphology together with variations in the channel and floodplain roughness coefficients grain size characteristics and critical shear stress on measures of flood inundation the results showed that the bed elevation modifications generated by the simplistic equations reflected an approximation of the observed patterns of spatial erosion that enveloped observed erosion depths the effect of uncertainty on channel long profile variability only affected the local flood dynamics and did not significantly affect the friction sensitivity and flood inundation mapping the results imply that hydraulic models generally do not need to account for within event morphodynamic changes of the type and magnitude of event modelled as these have a negligible impact that is smaller than other uncertainties e g boundary conditions instead morphodynamic change needs to happen over a series of events to become large enough to change the hydrodynamics of floods in supply limited gravel bed rivers such as the one used in this research

detailed simulation of morphodynamics 2 sediment pickup transport and deposition the paper describes a numerical model for simulating sediment transport with eddy resolving 3 d models this sediment model consists of four submodels pickup transport over the bed transport in the water column and deposition all based on a turbulent flow model using large eddy simulation the sediment is considered as uniform rigid spherical particles this is usually a valid assumption for sand bed rivers where underwater dune formation is most prominent under certain shear stress conditions these particles are picked up from the bed due to an imbalance of gravity and flow forces they either roll and slide on the bed in a sheet of sediment or separate from the bed and get suspended in the flow sooner or later the suspended particles settle on the bed again each of these steps is modeled separately yielding a physics based process model for sediment transport suitable for the simulation of bed morphodynamics the sediment model is validated with theoretical findings such as the rouse profile as well as with empirical relations of sediment bed load and suspended load transport the current model shows good agreement with these theoretical and empirical relations moreover the saltation mechanism is simulated and the average saltation length height and velocity are found to be in good agreement with experimental results

a method for estimating the mean bed load flux in braided rivers prediction of bed load flux remains a significant problem in understanding braided river morphodynamics for geomorphic and engineering applications two sets of data from laboratory experiments on braided networks performed at the university of trento italy and at the university of alberta canada provide the basis for development of a dimensionless bed load function and for testing a simple predictive model measured total sediment transport rates time averaged at equilibrium channel configuration collapse to a single dimensionless relationship based on dimensionless stream power bed load fluxes predicted by the parker and bagnold functions and cross section average hydraulic parameters under predict the bed load flux particularly at low shear stress this is consistent with previous observation and theory demonstrating the significant influence of transverse variability of the hydraulic parameters in controlling and predicting bed load flux a simple method for adjusting for this lateral variation is proposed for computing the sediment transport rate using topographic cross sections of braided rivers results show good agreement with the measured values suggesting that simple assumptions combined with the mean morphology of the channel may be sufficient to estimate mean bed load flux model predictions also highlight the significance of active bed width rather than bed shear stress as a fundamental ingredient in the prediction of the bed load rate and therefore as an important morphological property to be modelled the model also predicts similar behaviour in the at a station variability of bed load and in the importance of variation of active width relative to bed shear stress in the transport process

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

bed load texture in an alpine gravel bed river the spatial and temporal variations in bed load texture measured in a gravel bed river with a helley smith sampler are compared with its bed material texture most measurements were undertaken at low excess shear stress with low bed load discharge over an armored bed cross sectionally averaged fractional bed load discharge increases with water discharge but the explanation of the variance in fractional discharge is low 20 40 cross sectional distribution of shear velocity explains in part the spatial variation in bed load texture because local hydraulic parameters are weak predictors of fractional bed load discharge for the granule pebble range at nonequilibrium conditions it reinforces the hypothesis that this size range which comprises the bulk of bed load derives from upstream sources temporal variations in the cross sectional distribution of bed load texture are shown to depend on variations in bed topography and local shear stress we demonstrate that the dominance of granule pebble fractions is in part related to the hiding behavior of smaller fractions

simple model for downstream variation of median sediment size in chilean rivers a simple theory is developed to account for the observed downstream variation of the median sediment size in chilean rivers based on a reach wise equilibrium sediment transport concept the theory makes use of a bedload transport equation linked with a resistance equation to estimate the median sediment diameter as a function of channel slope with the flow reynolds number and bedload concentration as parameters both meyer peter and muller s and ackers and white s formulas are used alternatively as bedload equations a manning strickler type of formulation is used as a resistance relationship the resulting model is validated against field data corresponding to 150 rivers in central chile covering slopes in the range of 0 04 8 61 with median sediment size in the range of 0 3 250 mm despite the simplicity of the present theory and the somewhat bold assumptions made in its derivation the estimated variation of the median sediment size with channel slope follows the same trend as the field data most of the scatter of these data falls within the theoretical limits given by the estimated range of values of the parameters of the model

quantification of large uncertainties in fossil leaf paleoaltimetry 1 estimates of paleoelevation potentially constrain geodynamic models of continental deformation and inform interpretations of landscape and climate evolution one widely used paleobotanical approach reconstructs paleoelevation from the difference in estimated atmospheric enthalpy between a known sea level and a targeted coeval elevated fossil floral site enthalpy is estimated using climate leaf analysis multivariate program clamp on 31 leaf size and shape variables that have been calibrated in living forests errors related to clamp are significantly greater than often reported and there are many sources of large potential error related to this method that are either difficult to quantify or unquantifiable and are thus not documented here we quantify one significant bias toward underestimation of leaf area in the clamp data set 50 that affects all clamp climate estimates including enthalpy crucially errors in paleoelevation when the leaf size bias is included are in the range of 2 km or more at least 2 times the previous estimates and exceeding the plausible paleoelevations of many fossil sites previously published paleoelevations derived from this technique are unlikely to be accurate either in magnitude or in estimated error

the significance of paleotopography topographic change is one of the most informative measures of continental deformation yet precise records of past elevation are scarce to non existent in most orogenic belts recent advancement and new development of techniques to measure paleoelevation promise significant progress in understanding continental tectonic processes and how erosion acts on rising topography to shape the earth s surface outstanding issues in continental tectonics include understanding driving forces to deformation how strain is vertically partitioned in the lithosphere and how mass is redistributed or conserved in the lithosphere during deformation geodynamic and mechanical models that explore these topics make testable predictions of topographic evolution this review explores key examples of how paleotopography relates to outstanding issues in continental tectonics that motivate development of robust quantitative measures of paleoelevation

two dimensional two phase depth integrated model for transients over mobile bed abstractfast geomorphic transients may involve complex scenarios of sediment transport occurring near the bottom as bed load i e saltating sliding and rolling or as suspended load in the upper portion of the flow the two sediment transport modalities may even coexist or alternate each other during the same event especially when the shear stress varies considerably modeling these processes is therefore a challenging task for which the usual representation of the flow as a mixture may result in being unsatisfactory in the present paper a new two phase depth averaged model is presented that accounts for variable sediment concentration in both bed and suspended loads distinct phase velocities are considered for bed load whereas the slip velocity between the two phases is neglected in the suspended load it is shown that the resulting two phase model is hyperbolic and the analytical expression of the eigenvalues is provided the entrainment deposition of sediment between the bottom and the bed

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

average velocity of solitary coarse grain in flows over smooth and rough beds abstracta formula is derived for the prediction of the average velocity of a solitary coarse grain moving over a rigid flat channel bed to verify the theoretical consideration data collected in the present study and reported in the literature 811 sets in total are analyzed for typical bed roughness configurations the results show significant improvements in the prediction of solitary grain velocity for both smooth and rough bed conditions in comparison with other formulas available in the literature from the proposed formula it follows that for rough bed conditions the dimensionless grain velocity depends on the shields number and also the ratio of bed roughness height to the grain diameter the present study is limited to motion of solitary grains but the result obtained implies that bed load transport rate could be also affected by the equivalent bed roughness height even under mobile bed conditions and such effects may become pronounced for nonuniform sediments

discussion of protecting vertical wall abutments with riprap mattresses by a h cardoso and c m s fael the authors are to be commended for their experimental program and for the attempt to provide guidelines for safe design of scour countermeasures by means of launching aprons this is a technical field in which the existing literature is still relatively scarce in this discussion some remarks will be given about the upstream width wu of the launching apron refer to fig 12 of the paper under discussion the authors did not report specific experimentation in this respect indeed the upstream width of the mattress has received relatively scarce attention in works on riprap countermeasures experimental evidence has shown that for short abutments as well the values of the time averaged shear stress distribution in the corner region upstream of the abutment face are lower than that in the incoming reach rajaratnam and nwachukwu 1983 molinas et al 1998 dey and barbhuiya 2005 if the phenomenon is modeled at threshold conditions as is typically done in clear water scour experiments no scour would be expected upstream of the abutment face in all the regions with stress lower than that in the upstream reach experimental evidence on sediment motion during the scour process at short and intermediate abutments radice et al 2006 2008 has shown that at the beginning of the erosion process the particle motion is most intense at the abutment nose where scour starts in contrast grain motion is almost negligible at the junction between the duct and abutment walls junction region here an appreciable rate of scour depth is observed only after the scour hole whose point of maximum depth is typically at the obstacle nose has reached a significant transverse slope in terms of design of scour countermeasures protecting the sediment bed around the abutment nose might be sufficient to prevent the scouring process an experimental test of local scour at a protected abutment was performed to check this issue a rectangular duct with a length of 5 8 m and a width of 0 40 m was used the recess section of the duct was filled with uniform plastic grains with a characteristic size of d 3 6 mm and a relative density of 1 43 water discharge was 18 5 l s corresponding to the threshold value for incipient particle motion in the undisturbed bed the abutment model was a vertical plate with a length of 10 cm and a thickness of 1 cm fig 1 the experimental installation has been described in detail by radice et al 2009 who performed an identical scour experiment without abutment protection in that study the possibility of comparing scour data taken under freesurface and covered flows was also demonstrated in the present experiment the sediment bed around the abutment nose was protected by means of a square plate as shown in fig 1 the plate dimension was 20 cm along both the flow and transverse directions plate thickness was 1 cm the plate was roughened gluing on its upper surface sediments identical to those of the loose bed thus the resulting thickness of the countermeasure was 1 4 mm the described protection device is actually a rough collar installed at the level of the original sediment bed however at scour initiation the collar is likely to behave similarly to a launching apron with an elevation identical to that of the protected sediment bed therefore the following observations on scour initiation should not be significantly affected by the different configuration of the countermeasure at the beginning of the process some sediment motion was evident in the junction region fig 2 in this region the timeaverage shear stress is expected to be smaller than the threshold value it is therefore reasonable to assume the motion events as due to the peak stress values during the motion events the grains assumed directions opposite to that of the incoming flow consistent with the structure of the principal vortex the sediment particles moved downstream of the abutment passing over the protection plate the grain motion in the junction region resulted in a weak but nonnegligible scour rate some particles coming from the upstream reach can be recognized this is consistent with the definition used here of incipient particle motion which corresponds to a weak sediment transport condition dimensionless sediment transport rate per unit width 6 10 5 after about 3 min of run time fig 3 the junction region scour depth exceeded the thickness of the protection plate and the sediments

sediment transport and channel adjustments associated with dam removal field observations 1 this study documents changes in channel geometry bed level profile and bed grain size distribution and their relations with the sediment transport at the reach scale following the removal of a low head dam after the removal net sediment deposition occurred downstream of the dam and net erosion occurred in the reservoir but approximately less than 1 of the sediment stored in the reservoir was transported downstream no bank erosion was evident either upstream or downstream of the dam bed deposition and scouring in the reservoir accounted for a decrease in the bed slope of 30 the stations downstream of the dam had surface bed material sizes at least 40 finer than preremoval conditions however the sediment transport rates downstream of the dam were not significantly different from predam to postdam removal or from an upstream control overall the removal of the dam had only minor effects on the channel adjustment downstream of the dam a simple analysis linking transport to channel geometry explains this effect

transition between two bed load transport regimes saltation and sheet flow in the saltation regime where bed shear stress is low bed load moves by sliding rolling and saltating along the bed while in the sheet flow regime where bed shear stress is high it travels by a combination of saltation and sheet flow in this paper a theoretical model is developed for predicting the onset of the sheet flow regime as shear stress increases this model is based on a new variable pb representing the proportion of grains on the bed that are entrained as bed load the model yields the equation pb 2 56g 3 in which g 1 c dimensionless bed shear stress and c critical value of at which grains begin to move the equation shows that t which is the value of at the onset of the sheet flow regime and is assumed to occur when pb 1 is around 0 5 with the exact value controlled by c for example when c 0 045 t 0 52 the theoretical model is verified by performing a nonlinear regression analysis on data from 285 flume experiments additional flume experiments with a high speed video hsv system result in consistent values of for the onset of the sheet flow regime which support the theoretical model the hsv images further reveal that 1 the sheet flow regime is characterized by granular sheets or laminations and 2 a zone of mixed saltation and rolling grains exists not only in the saltation regime but also in the sheet flow regime

paleoclimatic estimates from tertiary leaf assemblages a primary obstacle to evaluating numerical modeling of tertiary nonmarine climates has been the significance and reliability of proxy data sloan barron 1990 lacking direct measurements of paleoclimatic parameters inferred paleoclimatic values are based on substitute proxy sources such as fossils or isotopes are proxy data significant that is have they been calibrated in modern environments and to what level is the calibration this is the problem of accuracy validity in the statistical sense second are the proxy data reliable can two workers or even the same worker consistently arrive at the same estimates using the same data set this is the problem of precision repeatability can these two problems be resolved quaternary palynologists have used the concept of transfer functions a methodology originally developed for foraminifera imbrie kipp 1971 applied in palynology a response surface for each palynomorph taxon is constructed for the environmental variables under consideration these transformations can then be subjected to a number of different kinds of multivariate analyses including ordination methodologies bartlein et al 1986 webb bryson 1972 these transfer functions can work for quaternary and especially the lateand post glacial of the last 20 to 30 thousand years pollen assemblages because in most regions where the methodology has been applied the flora is of known diversity and the equivalency of a given palynomorph species to one or a few extant species can be reasonably assumed even in the late neogene 1 5 to 10 million years ago however this assumption can no longer be made we know that the palynomorph assemblages contain exotic genera mccartan et al 1990 and the presence of exotic and or extinct species

evaluation of bed load transport formulae using field evidence from the vedder river british columbia abstract bed load transport formulae have not been tested extensively over medium spatial and temporal scales the lack of such testing is undoubtedly due to a paucity of field data available for testing at these scales extensive transport morphologic and discharge data available for a 10 year period along an 8 km study reach of the vedder river british columbia are used to test the predictive capabilities of bed load transport formulae at medium scales the transport data were obtained using the morphologic approach which is based on the premise that changes in channel morphology reflect the transfer of sediment such transport estimates can be made over larger spatial and temporal scales than is possible using traditional measurement techniques this study focuses on evaluating the original and revised versions of the bagnold stream power formula the meyer peter and muller formula and a stream power correlation overall the formulae are found to underpredict gravel transport rates for the vedder river the discrepancy is particularly pronounced in 1982 1983 and 1987 1990 which are periods during which significant dredging occurred dredging activity may have loosened the bed structure or resulted in a disequilibrium morphology thereby increasing sediment movement analysis is undertaken to assess how the use of mean daily discharge vs 15 min increment discharge series affects transport predictions results show that only the meyer peter and muller formula is particularly sensitive to which discharge series is used in calculations modification of the shields parameter is found to significantly affect transport predictions although it cannot explain alone the discrepancies between field data and calculated results predictions of total deposition in the study reach are well within an order of magnitude for all equations the bagnold type formulae and the meyer peter and muller formula do not capture the relatively even distribution of deposition along the study reach surprisingly the simple stream power correlation captured this downstream pattern of deposition cumulative distributions of predicted bed load transport are found to be most realistic for the original and revised bagnold formulae results of this study do not suggest that one particular formula is consistently preferred

sea bed noises reveal role of turbulent bursting phenomenon in sediment transport by tidal currents in many engineering and sedimentological applications it is usual to relate sediment movement to the time averaged bed shear stress however the shear stress exerted on the sea bed by tidal currents is intermittent in nature due to the turbulent bursting phenomenon1 2 sediment movement at the sea bed also occurs in bursts3 4 however attempts to link these two processes have failed because of the poor temporal resolution of existing sediment transport measurement techniques recent experimental advances now make this possible and we describe here the first detailed observations of sediment movement and fluid turbulence in tidal currents flowing over sandy gravels these results show that high stress values are a necessary but not sufficient condition for bed load sediment movement and that form drag on individual particles may have greater dynamical significance than the stress this work also suggests that it may now be possible to describe sediment movement at a level which is deterministic in terms of the turbulence and at very much shorter timescales than have been used previously

hydraulic geometry of secondary channels of lower fraser river british columbia from acoustic doppler profiling 1 the hydraulics and morphology of secondary channels within the lower fraser river gravel reach were examined using data collected with an acoustic doppler profiler during the large 2002 freshet data were collected over an area of channel subreach for a range of subreach morphologies upstream mid and downstream as suggested by visual evidence at a station hydraulic geometry of subreach types stratified along gradients of width depth and velocity fish habitat is more abundant and more persistently available in the wide deep downstream subreaches but higher velocities preferred by some species occur in the mid stream and upstream subreaches additional high flow data used to develop bank full scaling relations classical downstream hydraulic geometry conformed well to a simple power law up to and including data points from the main channel however width and depth exponents deviated from classical results investigation suggests that the relations observed in this study approach expected relations for constant slope and channel boundary materials

paleoelevation estimates for the northern and central proto basin and range from carbonate clumped isotope thermometry 1 quantitative paleoelevation histories can help explain both why and how widespread cenozoic extension occurred in the basin and range province of western north america we present new estimates of preextensional paleoelevations for the northern and central basin and range using clumped isotope 47 thermometry of lacustrine carbonates collected from each region comparison of carbonate 47 derived mean annual air temperature maat estimates 16 c 20 c for the late cretaceous eocene sheep pass basin of east central nevada with published maat estimates for the eocene coastal northern sierra nevada 20 c 25 c suggests that the early paleogene sheep pass basin had a paleoelevation of 2 km such a modest paleoelevation suggests that either 1 the proto northern basin and range did not attain maximum paleoelevations of 3 4 km until the late eocene early oligocene or 2 the sheep pass basin was a local high relief 1 km setting contained within a 3 km orogenic highland nevadaplano similarity of 47 derived maat estimates 17 c 24 c for carbonates from the central basin and range and the near sea level southern sierra nevada bena basin indicate that middle miocene paleoelevations in the death valley region were 1 5 km these fairly low paleoelevations are incompatible with preextensional crustal thicknesses 52 km and indicate that mean elevation change was minor 500 m and lithospheric mass was not conserved during 100 neogene extension of the central basin and range but was instead likely compensated by synextensional magmatic additions to the crust

end member models for andean plateau uplift abstract diverse techniques have been applied over the past decade to quantify the uplift history of the central andean plateau ap in this study opposing models for surface uplift are evaluated including a rapid rise of 2 5 km 10 6 ma and a slow and steady rise since 40 ma these end member models are evaluated by synthesizing observations of the ap lithosphere and the history of deformation sedimentation exhumation magmatism uplift and fluvial incision structural and geophysical studies estimate variable shortening magnitudes 530 150 km involving cover to basement rocks an isostatically compensated thick crust 80 65 km high heat flow and zones of variable velocity and attenuation in the crust and mantle these observations have invoked interpretations such as a hot weak lithosphere partial melt crustal flow and perhaps current localized delamination but do not provide strong support for massive delamination required by the rapid uplift model deformation and associated exhumation began 60 40 ma and generally migrated eastward with consistent long term average shortening rates 12 8 mm yr in bolivia favoring the slow uplift model volcanic and helium isotope evidence show an ap wide zone of shallow mantle melting and thin lithosphere that has existed since 25 ma which is inconsistent with the rapid rise model that suggests lithospheric thinning occurred 10 6 ma paleoaltimetry data suggest a rapid 2 5 km elevation gain 10 to 6 ma but are equally consistent within error with a linear rise since 25 ma widespread fluvial incision 2 5 1 km occurred along the western flank since 11 8 ma and may be associated with surface uplift as proposed by the rapid rise model however the paleoaltimetry and incision data can also be explained by regional climate change associated with plateau uplift implications of these results for reconstructions of ap evolution are that 1 substantial deformation of a weak lithosphere is essential 2 ap growth has taken significantly longer 40 myr and was more uniform along strike 1500 km than previously appreciated and 3 the slow and steady uplift model is most consistent with available constraints we conclude that the rapid uplift model may be an overestimate and that a more protracted cenozoic uplift history is tenable

response of low angle dunes to variable flow current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments there are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides as a consequence the ability to predict bedform response to variable flow is rudimentary using high resolution multibeam bathymetric data this study explores the dynamics of a dune field developed by tidally modulated fluvially dominated flow in the fraser river estuary british columbia canada the dunes were dominantly low lee angle features characteristic of large deep river channels data were collected over a field ca 1 0 km long and 0 5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet yielding the most comprehensive characterization of low angle dunes ever reported the data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs then increasing as the tide rises and the flow velocities decrease bedform lengths do not appear to respond to the changes in velocity caused by the tides changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity indicating that changes in the bedform geometry lag changes in the flow the data reveal that lee angle slope responds directly to suspended sediment concentration supporting previous speculation that low angle dune morphology is maintained by erosion of the dune stoss and crest at high flow and deposition of that material in the dune trough