modeling the tor dotted crests bedrock edges and parabolic profiles of high alpine surfaces of the wind river range wyoming abstract broad low curvature surfaces common to many alpine landscapes and particularly well expressed in the laramide ranges of the western usa appear to be roughly in steady state with respect to the current surface processes uniform thin order 1 m regolith covers the crystalline bedrock with the exception of occasional tors at ridgecrests the surfaces are commonly edged by bedrock lips at the tops of cliffs that bound the intervening glacial troughs regolith production is low order 10 m year on bare bedrock and reaches a maximum under tens of centimeters of regolith all of these characteristics may be accounted for with a numerical model that is faithful to the periglacial surface processes presently operating on these surfaces hillslope transport is modeled assuming the dominant process is frost creep transport efficiency depends linearly upon local slope and appropriately vanishes in the absence of regolith frost frequency scales the rate of motion while the ratio of frost penetration depth to regolith thickness dictates the degree to which the process is curtailed by available regolith initial conditions include initial mean slope and bedrock roughness and a uniform regolith cover boundary conditions are imposed by dictating that the edges of the calculation space be lowered at a rate appropriate for glacial incision broad convex surfaces emerge over time scales of order 1 million years all surfaces rapidly decouple from the bounding glacial troughs as the high negative curvature at the edges disallows accumulation of regolith these bedrock edges lower at a few microns per year while the troughs lower at many times this rate as the bedrock edges therefore serve as the effective boundary condition for the remaining surface the surfaces operate independently of both lowering and widening of the glacial troughs for a reasonable set of transport and weathering rates the final steady state landscape is sensitive to the initial condition in particular the steeper the initial landscape the more likely tors are to develop as the high curvature disallows accumulation of regolith these tors in turn limit the lowering rate of the crest and the landscape retains significant local relief low relief initial conditions more likely lead to parabolic surfaces that lack tors that tors are more likely on the crests reflects the high initial curvature at the crest tors on the side slopes are eliminated the present high surfaces in the laramide ranges of the western usa imply operation of periglacial surface processes over millions of years the occasional tors imply a steeper rather than flatter initial landscape the strong decoupling of surfaces from glacial troughs justifies their use as local geomorphic markers that allow calculation of relief production since glacial incision was initiated on the other hand their present low curvature does not require a landscape history in which these surfaces were once joined as an initially widespread erosion surface

mound development as an interaction of individual plants with soil water erosion and sedimentation processes on slopes in the mediterranean region semi natural shrubland communities named matorral often present a discontinuous cover where isolated perennial plants alternate with bare inter plant areas in such ecosystems the patchy distribution of the vegetation is usually associated with microtopographic sequences of mounds that develop under isolated plants and break the overall slope continuity in this study the influence of three representative species of the mediterranean matorral rosmarinus officinalis stipa tenacissima and anthyllis cytisoides on slope microtopography is determined and the processes that take part in the development of microtopographic structures beneath the plant canopy are identified the influence of slope gradient plant species and plant parameters on the shape and height of microtopographic structures is also studied the shape of the microtopographic structures is described by using a two dimensional microprofilemeter and mound height is determined by measuring in the field a mound height index defined as the distance from the top to the bottom of the mound the results obtained show that plant species play a major role in the shape and height of the microtopographic structures whereas terrace type structures generally develop under anthyllis shrubs microtopographic forms associated with rosmarinus and stipa plants vary with slope gradient the almost symmetric mound type structures that develop under these two species on gentle slopes change into terrace type structures as slope gradient increases moreover statistically significant differences exist between the three species with regard to mound height mean values of mound height are 19 4 14 6 and 4 3 cm under the canopy of stipa rosmarinus and anthyllis respectively plant parameters essentially roughness and slope gradient have a significant influence on mound height index four main processes were identified as affecting mound development in the studied field site sedimentation differential interrill erosion differential splash erosion and bioturbation plant species interact in different ways with these processes according to their morphologies since stipa and rosmarinus plants are more efficient than anthyllis shrubs in controlling water erosion in retaining sediments and in modifying soil properties under their respective canopies they give rise to higher microtopographic structures that facilitate water and nutrient storage by plants on slopes copyright 2000 john wiley sons ltd

biomarkers as proxies for plant inputs to peats an example from a sub boreal ombrotrophic bog lipid distributions in modern peat forming plants were determined and compared to biomarkers recovered from a ca 2800 year old peat deposited in a dutch ombrotrophic bog the peat section spans a well constrained shift in local hydrology and vegetation and potential molecular proxies for plant inputs were directly tested against the macrofossil record based on the analyses of modern plants low molecular weight lmw n alkanes c23 c25 and high molecular weight n alkanes c33 are proposed as potential biomarkers for sphagnum and non sphagnum inputs respectively consistent with this in the bargerveen peat core lmw n alkane abundances increase and hmw n alkane abundances decrease coincident with the shift to sphagnum dominated peat additional potential proxies include the abundances of c22 alkanedioic acid and phytenyl phytenoate as sphagnum indicators and the abundances of the triterpenoids taraxer 14 ene and taraxast 20 ene as biomarkers for ericaceae rootlets

the elements and richness of particle diffusion during sediment transport at small timescales the ideas of advection and diffusion of sediment particles are probabilistic constructs that emerge when the master equation a precise probabilistic description of particle conservation is approximated as a fokker planck equation the diffusive term approximates nonlocal transport it looks upstream and downstream for variations in particle activity and velocities whose effects modify the advective term high resolution measurements of bed load particle motions indicate that the mean squared displacement of tracer particles when treated as a virtual plume primarily reflects a nonlinear increase in the variance in hop distances with increasing travel time manifest as apparent anomalous diffusion in contrast an ensemble calculation of the mean squared displacement involving paired coordinate positions independent of starting time indicates a transition from correlated random walks to normal fickian diffusion this normal behavior also is reflected in the particle velocity autocorrelation function spatial variations in particle entrainment produce a flux from sites of high entrainment toward sites of low entrainment in the case of rain splash transport this leads to topographic roughening where differential rain splash beneath the canopy of a desert shrub contributes to the growth of a soil mound beneath the shrub with uniform entrainment rain splash transport often described as a diffusive process actually represents an advective particle flux that is proportional to the land surface slope particle diffusion during both bed load and rain splash transport involves motions that mostly are patchy intermittent and rarefied the probabilistic framework of the master equation reveals that continuous formulations of the flux and its divergence the exner equation represent statistically expected behavior analogous to reynolds averaged conditions key topics meriting clarification include the mechanical basis of particle diffusion effects of rarefied conditions involving patchy intermittent motions and effects of rest times on diffusion of tracer particles and particle borne substances this article is protected by copyright all rights reserved

ice storms tree throw and hillslope sediment transport in northern hardwood forests in december 2008 694 trees uprooted within a 108 ha 1 08 km2 watershed in central massachusetts due to a severe ice storm resulting in the displacement of 1300 m3 of root material unconsolidated sediment and fractured bedrock overall we find that uprooting and tree throw is often grouped in clusters and cascades conifers displace more material than deciduous trees areas with abundant mature hemlock and steep slopes are more susceptible to tree throw with clusters as dense as 125 per hectare and failure is predominantly downhill suggesting that ice storms promote efficient downslope hillslope sediment transport in northern hardwood forests combining the recurrence interval of severe storms in new england 20 75 years with the forest response presented here we calculate a sediment transport rate of 2 5 10 5 m3 m 1 a 1 averaged over the entire watershed forest susceptibility to tree throw differed based on location in the watershed some areas experienced up to 30 higher than average sediment transport rates while others experienced no tree throw two severe storms following the 2008 ice storm hurricane in 2011 snow storm in october 2012 did not result in significant tree throw within the study area highlighting that the coupling of storm severity and forest susceptibility controls the amount of tree throw during a given forest disturbance in addition to recent tree throw from the 2008 ice storm widespread pit and mound microtopography in the study area indicates that tree throw is a recurrent process in this landscape two factors emerge that will influence future ice storms related hillslope sediment transport in the steep forested hillslopes of new england regional climate gradients and changing climate determine the size intensity and recurrence of ice storms forest management practices and health control the tree age and type copyright 2015 john wiley sons ltd

molecular characterization of fossil and extant dammar resin extracts insights into diagenetic fate of sesqui and triterpenoids abstract the composition of sesquiterpenoids and triterpenoids in the solvent extract of extant miocene and eocene dammar i e class ii resins has been determined and compared to investigate the vulnerability of these biomarkers to diagenesis molecular evidence e g absence of bicadinanes and low rock eval maturity values tmax

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

short term soil mixing quantified with fallout radionuclides soil mixing plays a significant role in contaminant transport carbon sequestration and landscape evolution yet the rates and driving mechanisms are poorly constrained here we use depth profiles and advection diffusion modeling of fallout nuclides to quantify differences in short term 7 be and weapons derived isotopes and quantify mixing with a steady state model of vertical 210 pb transport on a forested landscape in the bega valley in southeastern australia and on grasslands in marin county california where bioturbation is documented as the dominant sediment transport mechanism we calculate diffusion like mixing coefficients of 1 2 cm 2 yr 1 in montane forest soils of northern new england we observe little field evidence of short term mixing and find that the traditional advection diffusion model fails to describe 210 pb profiles because nuclide profiles here can be described with a simple model of litterfall organic matter decay and radioactive decay we argue that diffusion like processes are barely active on short time scales and that the advection diffusion model overestimates diffusion like transport while animal bioturbation and soil freezing cycles have little effect on the fate of elements in new england physical soil mixing drives transport at bega valley and marin county we suggest that the absence of soil stirring that we quantify in new england forests may explain the slow physical erosion here 0 2 cm k y relative to the actively bioturbated soils of bega valley and marin county 5 10 cm k y

grains in motion a review abstract this review paper aims to present a practical integrated procedure for the prediction of sediment transport rates in both the continental and marine environment based on the settling velocity of particles such studies have important applications in diverse fields such as civil and coastal engineering sedimentology and environmental geology where they can assist in flood control and the prevention of contaminant dispersal by wind and water as well as the siltation of dams and harbours the formation of placer deposits including gold diamonds and other heavy minerals is also controlled by sediment transport processes so that these studies can form the basis for more efficient exploration programs the first part of the paper discusses some basic principles important in sediment transport followed by an overview of published methods to determine the settling velocity of differently shaped particles including natural grains the application of settling velocity to predict the entrainment threshold of sediments on plane horizontal and inclined beds by unidirectional currents and oscillatory waves is then discussed which finally leads to the determination of sediment transport rates over plane and rippled beds the validity of this approach to natural conditions is tested against published field data where possible other widely used methods are also critically discussed pointing out severe problems in current sampling technology and the calculation of bedload transport in natural environments

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

stable isotopic variations in west china a consideration of moisture sources 1 in this study individual precipitation samples collected over 2 years at stations in different climatic regions of west china tibetan plateau region tianshan region and altay were analyzed for the stable isotopes of precipitation to improve our understanding of how vapor transport impacts the modern stable isotopic distribution our results identify regional patterns in both 18o and deuterium excess d excess defined as d 8 18o and in particular we have identified the northward maximum extent of the southwest monsoon over the tibetan plateau this demarcation is also the boundary for the fractionation effect of temperature on stable isotopes in precipitation the patterns we have identified are as follows 1 in the southern tibetan plateau along the southern slope of the himalayas our results show a distinct seasonality for both 18o and d excess as a result of the shift of summer monsoon moisture and winter westerly moisture transport the signals of 18o in the western tibetan plateau reveal that the region receives southwest monsoonal moisture in the east of the plateau stable isotopic variation shows alternation between monsoon intrusion and recycling of northern moisture 2 in contrast in tianshan there is an apparent temperature effect in 18o with enriched values occurring in summer and depleted values occurring in winter seasonal d excess values opposite to those observed in the southern tibetan plateau are controlled by differing seasonal evaporation conditions 3 in altay the most northern mountain region the seasonal 18o shows the same variation with that in tianshan region however d excess shows no apparent seasonal variation

inverting topography for landscape evolution model process representation 3 determining parameter ranges for select mature geomorphic transport laws and connecting changes in fluvial erodibility to changes in climate

on bagnold s sediment transport equation in tidal marine environments and the practical definition of bedload bagnold s sediment transport equation has proved to be important in studying tidal marine environments this paper discusses three problems concerning bagnold s transport equation and its practical application 1bagnold s suspended load transport equation and the total load transport equation with are incorrect from the viewpoint of energy conservation in these equations the energy loss due to bedload transport has been counted twice the correct form should be for suspended load transport and for total load transport with 2the commonly used bagnold s transport coefficient k varies as a non linear function of the dimensionless excess shear stress which can be represented best by the power law where the coefficient a and exponent b depend on sediment grain size d the empirical values of a and b for fine to medium grained sands are determined using guy et al s 1966 flume experiment data 3the sediment transport rates predicted from this equation are compared with bedform migration measurements in the flume and the field this comparison shows that the sediment transport rates measured from bedform migrations are higher than the predicted bedload transport rates but comparable to the calculated total load bedload plus intermittent suspended load transport rates this indicates that bedform migration involves both bedload and intermittent suspended load transport as a logical conclusion bedform migration data should be compared with bagnold s total load transport equation rather than with his bedload transport equation in this respect the term bed material might be more appropriate than the term bedload for estimating sediment transport rate from bedform migration data the sediment transport rates predicted from this modified bagnold transport equation are in good agreement with field measurements of bedform migration rates in four individual tidal marine environments which cover a wide range of sediment grain size flow velocity and bedform conditions ranging from small ripples megaripples to sandwaves

polar aromatic biomarkers of miocene aged chukurovo resinite and correlation with a progenitor macrofossil abstract functionalised aromatic constituents of chukurovo resinite are compared here with the chemical composition of a macrofossil assigned paleobotanically as taxodium dubium sternb heer terpenoids and lipids of fossil wood tissue embedded in a clay sediment were extracted and analyzed for comparison the information was interpreted in relation to the biomarker compositions of different conifer families as well as to the effects of contamination by inward migration of organic matter from the adjacent sediments many of identified geolipids i e alkanes alkanols alkan 2 ones and steranes triterpanes have no chemosystematic value because they are ubiquitous in the plant kingdom ferruginol sugiol and products of their diagenetic transformations were identified as the dominant specific biomarkers in the resinite ferruginol and its analogues were the most abundant diterpenoids in taxodium dubium sample thus the biomarker composition of the extractable matter of the resinite strongly suggests that species of cupressaceae contributed significantly to the chukurovo paleoenvironment

reservoir theory for studying the geochemical evolution of soils 1 linking mineral weathering rates measured in the laboratory to those measured at the landscape scale is problematic in laboratory studies collections of minerals are exposed to the same weathering environment over a fixed amount of time in natural soils minerals enter are mixed within and leave the soil via erosion and dissolution leaching over the course of soil formation the key to correctly comparing mineral weathering studies from laboratory experiments and field soils is to consistently define time to do so we have used reservoir theory residence time of a mineral as defined by reservoir theory describes the time length between the moment that a mineral enters via soil production and leaves via erosion and dissolution leaching the soil age of a mineral in a soil describes how long the mineral has been present in the soil turnover time describes the time needed to deplete a species of minerals in the soil by sediment efflux from the soil these measures of time are found to be sensitive to not only sediment flux which controls the mineral fluxes in and out of a soil but also internal soil mixing that controls the probability that a mineral survives erosion when these measures of time are combined with published data suggesting that a mineral s dissolution reaction rate decreases during the course of weathering we find that internal soil mixing by partially controlling the age distribution of minerals within a soil might significantly alter the soil s mass loss rate via chemical weathering

particle size evidence of estuary evolution a rapid and diagnostic tool for determining the nature of recent saltmarsh accretion abstract a conceptual model of saltmarsh sedimentation based on high resolution particle size analysis has been tested on short cores c 0 5 m of known age from the dee estuary nw england uk here two components of the particle size distribution psd are interpreted as the traction load deposited by the faster tidal flow velocities fast tide and the suspension load that settles during the turn of the tide slow tide the feasibility of this model for diagnosing the driving mechanism of estuary evolution in both time and space is tested with reference to historical evidence of saltmarsh accretion up core trends in dated saltmarsh cores and the psds of present day saltmarsh surface sediments cores that show an up core progression from very fine skewed to near symmetrical psds are interpreted in the context of estuary infilling due to a positive sediment budget sediment surplus whilst those that show a persistence of near symmetrical very poorly sorted mesokurtic particle size distributions in the fine to very fine silts size range are considered to be the result of slow tide sedimentation the influences of the two end member styles of saltmarsh accretion i e i infilling due to sediment surplus and ii slow tide settling linked to sea level exhibit spatial and temporal trends as predicted particularly in cores from mid and lower saltmarsh locations the upper saltmarsh cores also show evidence of estuary infilling due to slow tide sedimentation at rates in excess of sea level rise the results confirm that the diagnostic approach can be applied as a pre filtering method for assessing the suitability of saltmarsh sediments for reconstructing sea level trends and for providing input data for improved estuary morphological modelling

the illusion of diffusion field evidence for depth dependent sediment transport soil covered upland landscapes are common in much of the habitable world and our understanding of their evolution as a function of different climatic tectonic and geologic regimes is important across a wide range of disciplines erosion laws direct quantitative study of the processes shaping earth s surface and form the basis of landscape evolution modeling but are based on limited field data here we use in situ produced cosmogenic 1 0 be and 2 6 al concentrations from granitic saprolite to quantify an exponential decline in soil production with increasing soil thickness for a new field site in point reyes california results are similar to soil production functions from two different previously studied field sites and are used with extensive measurements of soil thickness to quantify depth integrated sediment transport flux plots of calculated sediment fluxes against the product of soil depth and hillslope gradient provide the first field based evidence that soil transport is a nonlinear depth dependent function data from all sites suggest that the widely used linear diffusion equation is only appropriate for shallow gradient convex up regions while the depth dependent transport law is more broadly applicable quantifying both the mobile soil thickness and landscape morphology is therefore critical to understanding how landscapes evolve

toward process based modeling of geochemical soil formation across diverse landforms a new mathematical framework we present a mathematical model that integrates geochemical and geomorphic processes responsible for soils elemental and mineralogical evolution on diverse landforms eroding to depositional to level grounds this new model combines a hillslope sediment mass balance and a soil geochemical mass balance we model soils as the sum of a physically disturbed zone pdz and the underlying physically undisturbed but chemically altered zone caz the model considers processes including the production of pdz weathering front propagation mineral specific dissolution colloidal translocation and colluvial transport thus this study serves to 1 review preexisting models of pedogenic processes and to 2 offer a framework to integrate the geochemical and geomorphic processes active in soils we further discuss the implications of our model in 1 scaling chemical weathering reactions from mineral grains to pedons to soil catenas 2 understanding the emergence of geochemical soil catenas and 3 coupling physical and chemical weathering processes

influence of chemical denudation on hillslope morphology 1 models of hillslope evolution involving diffusion like sediment transport are conventionally presented as an equation in which the changes in land surface elevation or soil thickness are balanced by the divergence of soil transport and tectonic uplift soil production or both these models typically do not include the loss or gain of mass in hillslope soils due to processes of chemical weathering and deposition we formulate a more general depth integrated equation for the conservation of soil mass on a hillslope that includes a term representing chemical deposition or denudation this general depth integrated equation is then simplified to determine the one dimensional form of a steady state hillslope which experiences both mechanical and chemical denudation the differences in morphology between hillslopes only experiencing diffusion like mechanical sediment transport and hillslopes experiencing both diffusion like mechanical sediment transport and chemical denudation are explored under the conditions of a downslope increase in local soil lowering rate due to chemical weathering the hillslope profile will depart from the parabolic shape predicted by models that incorporate only linear diffusion like mechanical sediment transport in addition hillslopes that experience both chemical and mechanical denudation may have a convex concave profile at steady state a necessary condition for such steady state profiles is that the chemical denudation rate must exceed the mechanical denudation rate we further suggest that combinations of other physical parameter values such as total denudation rate average soil depth sediment diffusivity and the increase in soil depth away from the divide that lead to steady state convex concave hillslope profiles may exist in a wide variety of natural settings

bedforms and bed material transport pathways in the changjiang yangtze estuary abstract bed features were mapped using a thermal depth recorder and a side scan sonar in the changjiang yangtze estuary and flows were observed and bed surface materials were sampled to investigate bed material transport pathways distinct scales and dimensions of dunes were observed in terms of the classification scheme of ashley ashley g m 1990 classification of large scale sub aqueous bedforms a new look at an old problem journal of sedimentary research 61 160 172 forming a dune set in the flood season large dunes occurred predominately in the surveyed area of the estuarine zone and two dimensional dunes predominated in the dry season while three dimensional dunes prevailed in the flood season sharp lee sides of dunes have low angles indicating a significant suspended load transport for the bedform migration and the majority of them face down estuary reflecting the controlling process by the ebb current the bed material migrations in terms of relative maximum gross transport show a satisfactory agreement with the sonar mapping in the dry season the relative maximum gross transport as an independent estimator of migration direction can be used to effectively determine the bed material transport directions in the changjiang estuary

an evaluation of bagnold s dimensionless conefficient of proportionality using measurements of sandwave movement abstract only a few observations are currently available from the tidal marine environment which can be used to evaluate sediment transport formulae research carried out on sandwave movement indicates that most of the sediment transport is restricted to the crestal area mean rates of sediment transport were calculated from volumetric changes between successive slack waters over a nine day period spanning spring tides the results were used in conjunction with boundary layer flow measurements to calculate the threshold velocity for the movement of sediment and also to evaluate bagnold s 1963 dimensionless coefficient of proportionality k comparisons are made with the flume data of guy et al 1966 for the appropriate sediment grain size the dependence of k upon normalised excess shear stress was found to be weaker than that suggested by sternberg 1972 within the range of flow velocities considered there was no indication that k tended towards a constant at high flow velocities

introduction to special section on stochastic transport and emergent scaling on earth s surface rethinking geomorphic transport stochastic theories broad scales of motion and nonlocality 1 in many geomorphic transport systems the time and length scales of motion vary widely particles can be trapped for both short and long periods of time and they can travel large or small distances in very short intervals of time to model such systems we need fresh conceptual and mathematical formalisms the goal of this collection of papers is to challenge existing thinking in geomorphic transport by putting forward new ideas and theories for environmental fluxes from particle transport in a single stream to landslide debris mobilization sediment and water transport on hillslopes dynamic transport on river networks and interpretation of sedimentary deposits over geologic time advanced stochastic theories of transport are proposed the notion of nonlocal flux is introduced and fractional advection diffusion equations are explored as possible models of geomorphic transport

holocene evolution of bottom sediment distribution on the continental shelves of the bohai sea yellow sea and east china sea abstract coastline shifts due to transgression and regression can remodel tidal fields of continental shelves and this can control transport of sediments and modulate sediment distribution accordingly tidal currents have become the dominant hydrodynamic processes on the continental shelves of the bohai sea yellow sea and east china sea byecs since the transgression after the last glacial maximum lgm to examine the evolution of the bottom sediment distributions on the continental shelves of the byecs we simulated patterns of tides and tidal currents sediment transport and bottom sediment types sand mud and mixed sediments for five periods corresponding to sea level lowstands of 80 m 52 m and 30 m below present the holocene transgression maximum htm and the present the simulation shows that both sediment transport and shelf sediment distribution patterns were controlled by the strength type and asymmetry of tidal currents in the byecs since the lgm evolution of shelf sediment distribution patterns occurred in two stages 1 sediment emplacement and formation stage before the htm and 2 local adjustment after the htm the marked changes in coastline configuration since the lgm are the dominant factor controlling tide and tidal current evolution distribution of shelf sediment types in the byecs is closely related to tidal current fields during transgression after the lgm

terpenoids in surface soils from different ecosystems on the tibetan plateau abstract realizing the potential of terpenoid biomarkers as an unequivocal land ecosystem and floral diversity indicator calls for work to establish a direct link between the terpenoids extracted from the plants and those found in the underlying soils to this end we have characterized the triterpenoid profile of soils and vegetation along two altitudinal transects representing very different ecosystems the first transect comprising 31 sample sites was on the eastern slopes of mt gongga eastern tibetan plateau rising from 1230 m to 4500 m above sea level an area with a temperate monsoonal climate the second transect sampling 29 sites was on the northern slopes of mt west kunlun a region characterized by montane desert meadow and alpine steppe located between 1300 m and 5050 m above sea level the dominant terpenoid biomarkers polycyclic triterpenoids of the taraxerane oleanane friedelane ursane lupane glutinane and lanostane series identified in the soils were found to be consistent with the overlying vegetation however the discovery of some unusual triterpenoids including the pentacyclic triterpene 3 methyl ethers ptmes d a friedo 2 3 secoolean 2 3 dioic acid methyl 3 acetoxylup 20 29 en 28 oate 24 methylenecycloartan 3 one 9 19 cyclolanostan 3 yl 24 methylene acetate 3 methoxy 9 lanosta 7 24 dien 26 23 olide and 3 methoxy 9 lanost 7 en 26 23 olide in the gongga soils does not match the current vegetation and may be indicative of a long vanished forest type vegetation thus soil biomarkers may be a useful tool in the reconstruction of palaeo vegetation

statistical description of slope dependent soil transport and the diffusion like coefficient 1 for hillslopes undergoing diffusive soil transport it is often assumed that the soil flux is proportional to the local land surface gradient where the coefficient of proportionality is like a diffusion coefficient inasmuch as transport involves quasi random soil particle motions related to biomechanical mixing and similar dilational processes a slope dependent relation arises from a balance between particle fluxes that tend to loft a soil and gravitational settling of particles into available pore space a specialized form of the fokker planck equation adapted to such particle motions clarifies how the particle flux involves advective and diffusive parts this in turn contributes to a kinematic description of the diffusion like coefficient ingredients of this coefficient include an active soil thickness a characteristic particle size the porosity in excess of a consolidated porosity and the rate of particle activation as a function of depth these last two ingredients vertical porosity structure and activation rate in effect characterize the magnitude and frequency of settling particle motions related to biological activity and thereby set the rate constant of the transport process the significance of land surface slope is that it is a measure of the downslope component of slope normal lofting that is balanced by settling because the diffusion like coefficient contains the soil thickness the analysis suggests that the soil flux is proportional to the depth slope product the analysis is consistent with published profiles of soil creep displacement and with published estimates of soil flux obtained by downslope integration of soil production rates for hillslopes in california and australia

erosion rates in the southern oregon coast range evidence for an equilibrium between hillslope erosion and sediment yield the relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes in landscapes containing hillslopes crenulated by alternating topographic noses and hollows estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows hollows act as local traps for a portion of the colluvium transported down hillslopes and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area analysis of colluvial deposits in nine oregon coast range hollows has yielded average colluvial transport rates into the hollows of about 35 cm3cm 1yr 1 and average bedrock lowering rates of about 007 mm yr for the last 4000 to 15000 yr these rates are consistent with maximum bedrock exfoliation rates of about 0 09 mm yr calculated from six of the hollows supporting the interpretation that exfoliation rates limit erosion rates on these slopes sediment yield measurements from nine coast range streams provide similar basin wide denudation rates of between 0 05 and 0 08 mm yr 1 suggesting an approximate steady state between sediment production on hillslopes and sediment yield in addition modern sediment yields are similar in basins varying in size from 1 to 1500 km2 suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape

the potential influence of dust flux and chemical weathering on hillslope morphology convex soil mantled carbonate hillslopes in the eastern mediterranean abstract convex soil covered hillslopes are ubiquitous in various tectonic and climatic settings and their morphologic characteristics can be significantly altered by dust flux and chemical weathering carbonate hillslopes across the eastern mediterranean display a classic convex morphology despite high rates of dust deposition which are apparently similar in magnitude to denudation rates and despite a highly soluble bedrock lithology these high rates of dust flux and bedrock dissolution result in soil composition which is strikingly different from the underlying bedrock in this study we apply a modified regolith mass balance equation which includes dust input and chemical depletion and utilize a combination of field work and geochemical methods immobile and major elements xrd to estimate the fraction of dust derived materials in the soil and the fraction of the soil that was lost via dissolution soil and bedrock were sampled at 7 eastern mediterranean study sites across a prominent north to south gradient in both precipitation 250 to 900 mm yr 1 and dust flux 150 to 40 g m 2 yr 1 and compared with dust composition our results indicate that the dust fraction in the soil correlates with modern measurements of dust deposition rates and decrease from nearly 100 of the 2 mm indicating that mechanical weathering of the underlying bedrock contributes to regolith formation and plays a role in shaping carbonate hillslopes using a commonly used soil transport model we show that the observed dust fraction and chemical weathering can potentially account for a 50 change in hillslope curvature furthermore the predicted steady state hilltop curvature based on our results fits well the observed curvature based on high resolution lidar derived topographic data our results highlight the potential importance of dust and chemical weathering in soil production formulations and hillslope evolution models and we propose that these contributors to soil mass balance could also be relevant for silicate terrain in addition we also demonstrate that the source material of mediterranean soils varies with environmental factors such as rainfall dust deposition rates and bedrock mechanical properties

cosmogenic nuclides topography and the spatial variation of soil depth abstract if the rate of bedrock conversion to a mobile layer of soil depends on the local thickness of soil then hillslopes on uniform bedrock in a landscape approaching dynamic equilibrium should be mantled by a uniform thickness of soil conversely if the depth of soil varies across an actively eroding landscape then rates of soil production will also vary and consequently the landscape will not be in morphologic equilibrium the slow evolution of hillslopes relative to the tempo of climatic variations and tectonic adjustments would suggest that local morphologic disequilibrium may be expected in many landscapes here we explore this issue of equilibrium landscapes through a previously developed model that predicts the spatial variation in thickness of soil as a consequence of the local balance between soil production and erosion first we confirm the assumption in the model that soil production varies inversely with the thickness of soil using two independent methods one method uses the theoretical prediction that at local steady state soil production equals removal the depth of soil should vary inversely with hillslope curvature the second method relies on direct measurements of in situ produced concentrations of cosmogenic 10 be and 26 al in bedrock at the base of the soil column for our study site in northern california the two methods agree and yield the expression that the rate of soil production declines exponentially with the thickness of soil from 0 077 mm year with no soil mantle to 0 0077 mm year under 1 m of soil we then use this function of soil production in a coupled production and diffusive model of sediment transport to explore the controls on the spatial variation of the depth of soil on four separate spur ridges noses where we measured the data for the function of soil production model predictions are sensitive to boundary conditions grid scale and run time nonetheless we found good agreement between predicted and observed depths of soil as long as we used the observed function of soil production the four noses each have spatially varying curvature and consequently have varying depths of soil implying morphologic disequilibrium we suggest that our study site has been subjected to a wave of incision and varying intensities of erosion because of tectonic and climatic oscillations that have a frequency shorter than the morphologic response time of the landscape

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

microtopography as an indicator of modern hillslope diffusivity in arid terrain diffusion of topography is normally considered a smoothing process but at the scale of the diffusive disturbance diffusion becomes a roughening process roughening is exemplified by topographic features associated with disturbances such as animal burrows hoof prints of grazing animals and small landslides here called large scale processes diffusive processes that make small or indistinct topographic landmarks such as rain splash and rheological creep here called small scale processes tend to erase these roughness elements the ratio of the small scale diffusion coefficient to the large scale diffusion coefficient can be estimated by a measurement of the areal density of large scale disturbances in lightly vegetated arid terrain small scale diffusion is dominant unless large scale roughness elements cover a large fraction of the surface the values of large scale and small scale modern diffusion coefficients can be estimated if the rate of generation of large scale disturbances is known such estimates are performed for a burrowed fault scarp in nevada

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

process based model linking pocket gopher thomomys bottae activity to sediment transport and soil thickness burrowing organisms assist in shaping earth surfaces and are simultaneously affected by the environment they inhabit however a conceptual framework is not yet available to describe this feedback we introduce a model that connects the population density of soil burrowing animals to sediment transport via energy the model combined with avail able data from california hillslopes where soil erosion is driven by pocket gophers thom omys bottae suggests that a gopher annually expends 9 kj of energy or 1 of re ported burrowing energy expenditure in generating sediment transport the model is used to evaluate the case that gophers prefer to populate thicker soils the results suggest that this behavior may drastically dampen the spatial and temporal variations of soil thickness and gopher populations implying that burrowing organisms may create landscapes dis tinct from those affected by abiotic processes

comparisons of measured and predicted sediment transport rates in tidal currents abstract this paper describes bedload transport measurements in a large scale sedimentary system on the british continental shelf steady flow sediment transport theories are applied to oscillatory tidal currents and various equations are compared with measured transport rates from tracer dispersion experiments the effects of waves on both measured and predicted rates are briefly considered and the predicted directions of sediment movement compared with those inferred from sedimentological data

a process based model for colluvial soil depth and shallow landsliding using digital elevation data a model is proposed for predicting the spatial variation in colluvial soil depth the results of which are used in a separate model to examine the effects of root strength and vertically varying saturated conductivity on slope stability the soil depth model solves for the mass balance between soil production from underlying bedrock and the divergence of diffusive soil transport this model is applied using high resolution digital elevation data of a well studied site in northern california and the evolving soil depth is solved using a finite difference model under varying initial conditions the field data support an exponential decline of soil production with increasing soil depth and a diffusivity of about 50 cm 2 yr the predicted pattern of thick and thin colluvium corresponds well with field observations soil thickness on ridges rapidly obtain an equilibrium depth which suggests that detailed field observations relating soil depth to local topographic curvature could further test this model bedrock emerges where the curvature causes divergent transport to exceed the soil production rate hence the spatial pattern of bedrock outcrops places constraints on the production law the infinite slope stability model uses the predicted soil depth to estimate the effects of root cohesion and vertically varying saturated conductivity low cohesion soils overlying low conductivity bedrock are shown to be least stable the model may be most useful in analyses of slope instability associated with vegetation changes from either land use or climate change although practical applications may be limited by the need to assign values to several spatially varying parameters although both the soil depth and slope stability models offer local mechanistic predictions that can be applied to large areas representation of the finest scale valleys in the digital terrain model significantly influences local model predictions this argues for preserving fine scale topographic detail and using relatively fine grid sizes even in analyses of large catchments

early diagenesis of terrigenous triterpenoids and its implications for petroleum geochemistry abstract the distribution of triterpanes in sediments and crude oils is commonly used for oil oil and oil source rock correlation in petroleum geochemistry while isomer ratios of such compounds are applied as maturity parameters the triterpane pattern in terrestrially influenced geological samples is however remarkably less diverse than the triterpenoid skeletons occurring in the extant higher plant biosphere natural observations laboratory experiments and molecular mechanics calculations have revealed that acid catalysed double bond isomerization and skeletal rearrangement reactions of terrigenous triterpenoids during early diagenesis are the key to understanding the triterpane patterns in more matured geological materials examples studied in detail are the double bond isomerization of oleanenes and the subsequent hydrogenation of the products into oleanane and 18 oleanane and the transformation of taraxer 14 ene and lup 20 29 ene into oleanenes although the reactions are likely to be kinetically controlled the main products formed and ultimately preserved are the thermodynamically most stable ones the experimental results and natural observations have significant implications for the use of terrigenous triterpenoid compounds in petroleum geochemistry

constraining climatic controls on hillslope dynamics using a coupled model for the transport of soil and tracers application to loess mantled hillslopes south island new zealand 1 landscapes reflect a legacy of tectonic and climatic forcing as modulated by surface processes because the morphologic characteristics of landscapes often do not allow us to uniquely define the relative roles of tectonic deformation and climate additional constraints are required to interpret and predict landscape dynamics here we describe a coupled model for the transport of soil and tracer particles at the hillslope scale to illustrate the utility of this methodology we modeled the evolution of two synthetic hillslopes with identical initial and boundary conditions but different histories of climate induced changes in the efficiency of soil transport while one hillslope experienced an initial phase of rapid transport followed by a period of retarded transport the other hillslope experienced the opposite sequence both model hillslopes contain a subsurface layer of tracer particles that becomes exhumed and incorporated into the soil due to transport and mixing processes whereas the morphology of the two model hillslopes cannot be easily distinguished at the simulation conclusion the spatial distribution of tracer particles along the slope is distinctive for the two cases we applied the coupled model to our study site along the charwell river south island new zealand where tephra deposits within loess dominated soils have been exhumed and incorporated into an upper layer of bioturbated and mobile soil we reconstructed the late pleistocene hillslope geometry using soil stratigraphic data gathered along the study transect because bioturbation appears to be the predominant transport mechanism the efficiency of soil transport likely varies with time reflecting the influence of climate related changes in the dominant floral or faunal community the modeled evolution of hillslope form and tephra concentration along the study transect is consistent with observations obtained from topographic surveys and laboratory analysis of tephra concentrations in continuous core soil samples low transport rates are apparently associated with grass shrub dominated slopes during the late pleistocene whereas forest colonization during the holocene increased flux rates transforming flat locally incised slopes into broadly convex ones our results attest to the utility of coupled models for tasks such as deciphering landscape history and predicting the downslope flux of soil organic carbon

effects of vegetation change on interrill runoff and erosion walnut gulch southern arizona during the past 100 years grassland has been replaced by shrubland in many parts of the american southwest the effects of this vegetation change on interrill runoff and erosion are investigated by performing field experiments on small and large runoff plots located on contemporary grassland and shrubland hillslopes in walnut gulch experimental watershed the experiments indicate that the vegetation change causes runoff and erosion to increase in interrill areas by decreasing resistance to overland flow decreasing runon infiltration increasing the spatial heterogeneity of the plant canopy and possibly increasing the susceptibility of the soil to frost action increased runoff and erosion result in stripping of the soil a horizon the formation of desert pavement in intershrub areas and the development of rills fines remain and accumulate only under shrubs where they form islands of fertility shrubs are able to regenerate in these islands but it is difficult for any plants to become established in intershrub areas consequently there is an increase in the spatial heterogeneity of soil resources and this spatial heterogeneity is self perpetuating increasing spatial heterogeneity of soil resources is considered to be characteristic of the process of desertification

on the dynamics of sediment suspension by residual reynolds stresses confirmation of bagnold s theory bagnold s dynamic theory for sediment suspension requires that the immersed weight of suspended grains over unit bed area is supported by an upward directed residual reynolds stress yy arising from asymmetrical shear turbulence the present paper presents an analysis of previously published turbulence data which confirms the existence of this residual stress and indicates its generation in the lowermost part of the buffer layer of turbulent shear flows the magnitude of yy is estimated as about 0 3 yx calculations from experimental data on suspended fine sand transport over upper phase beds reveals that yy is in approximate equilibrium with the weight stress due to the suspended load

molecular characterisation of soil surface horizons with different vegetation in the vosges massif france the total lipid extracts tles from a series of 13 soil surface samples from sites covered by a stable vegetation for at least 150 years and located in the vosges massif france have been investigated in order to establish a molecular reference for soil surface horizons the tles are dominated by plant n alkyl lipids with distributions homologue predominance clearly discriminant with regard to the vegetation cover higher plant terpenoids present in varying relative abundances allow distinction between soils from grassland and oak fir and beech forests to be made furthermore the occurrence of some specific terpenoids seems to be restricted to a particular vegetation cover so they may therefore be used as diagnostic markers for tracing back past vegetation in ancient soils

geometry and kinematics of dunes during steady and unsteady flows in the calamus river nebraska usa the geometry and kinematics of river dunes were studied in a reach of the calamus river nebraska during day long surveys dune height length steepness migration rate creation and destruction were measured concurrently with bedload transport rate flow depth flow velocity and bed shear stress within a survey individual dune heights lengths and migration rates were highly variable associated with their three dimensional geometry and changes in their shape through time notwithstanding this variability there were discernible changes in mean dune height length and migration rate in response to changing discharge over several days changes in mean dune height and length lagged only slightly behind changes in discharge therefore during periods of both steady and unsteady flow mean dune lengths were quite close to equilibrium values predicted by theoretical models mean dune steepnesses were also similar to predicted equilibrium values except during high falling flows when the steepness was above that predicted variations in mean dune height and length with discharge are similar to those predicted by theory under conditions of low mean dune excursion and discharge variation with a short high water period and long low water period however the calculated rates of change of height of individual dunes vary considerably from those measured rates of dune creation and destruction were unrelated to discharge variations contrary to previous results instead creations and destructions were apparently the result of local variations in bed shear stress and sediment transport rate observed changes in dune height during unsteady flows agree with theory fairly well at low bed shear stresses but not at higher bed shear stresses when suspended sediment transport is significant

analysis of hillslope erosion rates using dated colluvial deposits hollows are sites of long term deposition of colluvium and contain a valuable record of the timing and rates of hillslope erosion a model is presented that uses measured depositional rates of colluvium in hollows to calculate transport rates of colluvium and bedrock lowering rates on the surrounding slopes this model has been applied to eight dated colluvial deposits in the clearwater river basin of western washington the calculated average transport rate is about 34 cm 3 cm yr and the calculated average bedrock lowering rate is about 0 04 mm yr equivalent to an average sediment yield of 90 t km 2 yr for the holocene there is significant variability in erosion rates between sites which may be due to local lithologic variations although the average values are similar to an independent estimate of modern erosion rates for this area multiple stratigraphic levels have been dated in five deposits and document that the deposits are cumulative and that deposition has been active through the

carbon isotope evidence for sedimentary miliacin as a tracer of panicum miliaceum broomcorn millet in the sediments of lake le bourget french alps abstract we report the determination of the carbon isotopic composition of miliacin olean 18 en 3 ol methyl ether extracted from the sediments of lake le bourget french alps it is compared with the 13 c value of miliacin extracted from panicum miliaceum broomcorn millet a c 4 plant and chionochloa sp a c 3 plant the 13 c value of sedimentary miliacin 21 5 is very close to that of miliacin extracted from bran 23 and seeds 23 5 of p miliaceum and significantly different from that of chionochloa sp 33 these results provide additional support for the use of sedimentary miliacin as a tracer of broomcorn millet a c 4 cereal cultivated since the bronze age around lake le bourget these findings illustrate the potential of this compound to reconstruct past agriculture from lake sediment archives finally considering the high abundance of miliacin in the bran of p miliaceum the compound could have been wind transported to the sediment during threshing and winnowing on the lake shore

particle transport over rough hillslope surfaces by dry ravel experiments and simulations with implications for nonlocal sediment flux 1 past studies of hillslope evolution have typically assumed that soil creep processes are governed by a linear relationship between local hillslope angle and transport distance the assumption of linear diffusion has fallen out of favor because when coupled with an expression of mass continuity it yields unrealistic hillslope profiles as a consequence a better understanding of the mechanics of sediment transport is needed here we report results from a series of flume experiments performed to investigate sediment transport by dry ravel a common soil creep process in arid and semiarid environments we find that at gentle slopes transport distances follow distributions characteristic of local transport as gradients steepen a fraction of the particles begins to exhibit nonlocal transport and that fraction increases rapidly with slope a stochastic discrete element model that couples an effective friction term with a shock term reproduces the results from the flume experiments suggesting that it can be used to explore the nature of particle transport on rough surfaces the model predicts that exponential distributions of transport distances on gentle slopes evolve into quasi uniform distributions on steep slopes and the transition occurs as slopes approach the angle of repose our results support previous findings that the angle of repose represents a threshold between friction and inertial regimes in addition we propose that the angle of repose represents a fuzzy boundary between local and nonlocal transport

dunes and associated sand transport in a tidally influenced sand bed channel fraser river british columbia dunes form annually on the sand bed of the tidally influenced south arm of fraser river british columbia bathymetric surveys along the center of the main channel throughout a snow melt freshet provided measurements of dune geometry and migration dune length height and steepness all increase with river discharge however lag between the highest flow conditions and development of the largest steepest dunes reflects the influence of antecedent flow conditions on dune geometry population averages of dune height and steepness ratio change more rapidly than dune length whilst coefficients of variation of dune height length and steepness ratio indicate high variability in dune geometry within the estuarine reach during periods of dune growth and decay unlike dune geometry dune migration rates display little lag with flow conditions the largest coefficients of variation for dune migration occur during periods of rapid change in discharge and tidal fall corresponding to the onset of rapid change in

soil creep problems raised by a 23 year study in australia in october 1965 and february 1966 55 young pits were installed in tropical northern territory nt and temperate new south wales nsw pits were monitored in 1968 1971 and 1974 also for the nt only in 1988 in each region half of the pits are on weathered granite and half on sandstone local relief is 30m or less and slopes are up to 20 annual rainfall is evenly distributed in the nsw sites 800 mm a 1 but is confined to the five to six month wet season in nt 1200 mm a 1 six pits suffered external disturbance and so were not analysed analysis of 160 rods in 49 undisturbed pits shows 1 vectorial movement generally not downslope parallel to the ground surface but dominated by a vertically downward component 2 significant uphill and vertically upward components of movement for many rods 3 a weak correlation between total movement and sine of slope 4 rapid movement during 1965 68 and slow movement thereafter 5 significantly higher creep rates on the nt granites than on all other sites perhaps because mound building termites are especially active there we conclude that our data do not support soil creep models which assume that all movement is downslope and slope parallel repeated long term measurements are essential to distinguish long term creep rates from the short term effects of disturbance copyright 1999 john wiley sons ltd

conifer and angiosperm biomarkers in clay sediments and fossil plants from the miocene clarkia formation idaho usa the aliphatic lipids and terpenoids of conifer and angiosperm macrofossils and the clay sediment from a new site p 37 of the miocene clarkia formation idaho usa were analyzed to evaluate the preservation of characteristic conifer and angiosperm biomarkers in the sediment series of aliphatic lipids terpenoids and steroids similar to the biomarkers found in type locality clarkia p 33 were the predominant compounds in the sediment and in the fossils long chain aliphatic lipids were major compounds in the fossil plants and the sediment but a differentiation of angiosperm and conifer sources is not possible due to their common distribution among all vascular plants in addition to previously reported terpenoids diterpenoids of a conifer origin and several angiosperm derived polar triterpenoids of the oleanane lupane ursane and friedelane classes are reported here for the first time from the clarkia sediments the conifer shoots taxodium glyptostrobus calocedrus contained characteristic conifer biomarkers such as abietane type diterpenoids while characteristic angiosperm triterpenoids were predominant in the angiosperm leaves betula quercus lithocarpus the biomarker compositions of the taxodium and glyptostrobus shoots match the terpenoid patterns previously reported from fossil seed cones of the same genera although conifer macrofossils contribute about 45 to the flora of site p 37 characteristic conifer biomarkers occurred in the sediment in only low amounts while the angiosperm derived triterpenoids were present in comparatively higher abundances the results indicate that the conifers are under represented compared to the angiosperms according to the terpenoid composition of the sediment extract this may be due to the presence of small angiosperm derived particles leaf detritus wax in the sediment and or migration of leaf waxes from the angiosperm leaves into the sediment in contrast the diterpenoids are trapped in the resinous woody tissue of the conifers and are thus disseminated less into the sediment

effect of precipitation regime on δ d values of soil n alkanes from elevation gradients implications for the study of paleo elevation we measured dd values of long chain n alkanes isolated from 30 surface soil samples along two elevation transects on the tibetan plateau differing in precipitation regime and water source the east asian monsoon precipitation dominates the wetter regime on the eastern slope from 1230 to 4300 m of gongga shan on the eastern tibetan plateau precipitation from the polar westerlies dominates the drier region on the slope from 1900 to 5000 m in the west kunlun shan on the northwestern tibetan plateau the decrease in dd value with elevation in the wetter region greatly exceeded that in drier region by 1 9 0 1 100 m and 1 4 1 0 100 m respectively the apparent fractionation between leaf wax and precipitation ewax p values in the wetter region ca 164 were more negative than those in drier region ca 125 above 3200 m we also measured dd values in leaves of six common living trees values from 287 to 193 from gongga shan ranging from about 2900 4200 m the abundance weighted average values of the nalkanes ddwax show a strong reverse correlation with sample source elevation r 2 0 78 for soils from 2 0 85 for soils from west kunlun shan above 3200 m suggesting that n alkane ddwax faithfully records the precipitation dd and that the isotopic altitude effect of precipitation controls ddwax altitudinal gradients in the mountains the data show a fairly strong monotonic dependency of n alkane dd values on elevation for the eastern plateau but a complex relationship between n alkane dd values and elevation for the northwestern plateau the ddwax values at sites below 3200 m from the kunlun shan area exhibit an unexpected positive correlation with elevation the study confirms the potential for using sediment ddwax values to reconstruct paleo elevation in wetter regions but suggests caution in applying the approach to dry regions our results also show it is essential to consider the intricacy of the pattern of atmospheric circulation and water sources and their influence on the lapse rate of dd values with elevation

oxygenated spiro triterpenoids possibly related to arborenes in sediments of a tropical freshwater lake abstract three novel 3 oxygenated cd spiro triterpenoids were tentatively identified as 13 15 spiro arbor 9 11 en 3 one 3 methoxy 13 15 spiro arbor 9 11 ene and 13 15 spiro arbor 9 11 en 3 ol in solvent extracts of sediments from lake valencia their proposed origin from higher plants is based on structural precursor product relationships and characteristics of the age distributions since the latest pleistocene

soil transport driven by biological processes over millennial time scales downslope soil transport in the absence of overland flow has been attributed to numerous mechanisms including particle by particle creep and disturbances associated with biological activity process stochasticity and difficulties associated with field measurement have obscured the characterization of relevant long term soil transport rates and mechanisms in a series of incised fluvial terraces along the charwell river south island new zealand we documented vertical profiles of tephra concentration and topographic derivatives along a hillslope transect to quantify soil transport processes along the undissected hilltop we observed a thin primary tephra layer ca 22 6 ka within loess deposits 80 cm below the landscape surface in the downslope direction the depth to the highly concentrated tephra layer decreases coincident with an increase in hillslope convexity which is proportional to landscape lowering rate if soil flux varies linearly with hillslope gradient exhumation of the tephra layer results from landscape lowering due to disturbance driven soil transport approximately 20 m downslope of the interfluve the depth to the tephra layer declines to 40 50 cm peak tephra concentrations decrease by a factor of 4 and tephra is distributed uniformly within the upper 40 cm of soil the transition from a thin highly concentrated tephra layer at depth to less concentrated widely distributed tephra in the upper soil may result from soil mixing and transport by biological disturbances along our transect the depth to this transition is 50 cm coincident with the rooting depth of podocarp and nothofagus trees that populated the region during much of the holocene our observations can be used to calibrate the linear transport model but more important they suggest that over geomorphic time scales stochastic bioturbation may generate a well mixed and mobile soil layer the depth of which is primarily determined by flora characteristics

bedform migration and bed load transport in some rivers and tidal environments reliable field data obtained by directly measuring bed load transport of fine to coarse grained bed material are extremely scarce mainly because of the difficulty of sampling accurately therefore the verification of bed load transport formulae is largely based on flume experiments which refer to unrealistic shallow water conditions in this study some bed load transport formulae were tested against data from natural environments as an alternative to ascertaining the bed load transport rate by sampling the bed load the transport rate was deduced from data on bedform height and bedform celerity for this purpose 43 sets of data from rivers representing a wide range of bed material bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings two formulae were used for the prediction of the bed load transport the formula of van rijn 1981 and the kalinske 1947 formula as approximated by elzerman frijlink 1951 and in the present study slightly modified for application to tidal waters both the bed load function of van rijn and the modified formula of kalinske frijlink require data which are easily obtained and that can be measured accurately at those stages of the flow when bed load transport was high the van rijn function tended to overestimate that transport for flow stages when bed load transport was low the opposite was true the modified kalinske frijlink function gave consistently good results 86 of the transport rates predicted using the river data were within 0 5 2 0 times the values actually measured

a generalized exner equation for sediment mass balance 1 the advance of morphodynamics research into new areas has led to a proliferation of forms of sediment mass balance equation without a general equation it is often difficult to know what these problem specific versions of sediment mass balance leave out to address this we derive a general form of the standard exner equation for sediment mass balance that includes effects of tectonic uplift and subsidence soil formation and creep compaction and chemical precipitation and dissolution the complete equation 17 allows for independent evolution of two critical interfaces that between bedrock and sediment or soil and that between sediment and flow by eliminating terms from the general equation it is straightforward to derive mass balance equations applicable to a wide range of problems such as short term bed evolution basin evolution bedrock uplift and soil formation and carbonate precipitation and transport dropping terms makes explicit what is not being considered in a given problem and can be done by inspection or by a formal scaling analysis of the terms scaling analysis leads directly to dimensionless numbers that measure the relative importance of terms in the equation for example the relative influence of spatial versus temporal changes in sediment load on bed evolution combining scaling analysis with time averaging shows how the relative importance of terms in the equation can change with timescale for example the term representing bed evolution due to temporal change in sediment load tends to zero as timescale increases

palaeotidal speeds and ranges estimated from cross bedding sets with mud drapes tidally formed cross bedding sets in which mud drapes are spaced out among sandy foresets occur in cretaceous1 4 eocene5 and holocene6 sands deposited subtidally by strongly asymmetrical sand waves a striking feature of some sets4 6 is that the horizontal drape spacing measured in the direction of sand wave advance varies cyclically on a time scale related to the spring neap tidal cycle as indicated by the numbers of drapes each drape forms part of a distinctive lithological couplet consisting of a group of sandy foresets recording avalanching on the steeper side of the sand wave followed by the drape itself typically divided into upper and lower parts by a centrally placed silt sand parting the drapes have been assigned to slack water but the groups of sandy foresets to episodes of vigorous flow the combination suggesting a quantitative model based on the tide here i show how the peak speeds and ranges of ancient tides can be estimated by combining an empirical bedload transport function with appropriate measurements from such cross bedding sets

trouble with diffusion reassessing hillslope erosion laws with a particle based model 1 many geomorphic systems involve a broad distribution of grain motion length scales ranging from a few particle diameters to the length of an entire hillslope or stream studies of analogous physical systems have revealed that such broad motion distributions can have a significant impact on macroscale dynamics and can violate the assumptions behind standard local gradient flux laws here a simple particle based model of sediment transport on a hillslope is used to study the relationship between grain motion statistics and macroscopic landform evolution surface grains are dislodged by random disturbance events with probabilities and distances that depend on local microtopography despite its simplicity the particle model reproduces a surprisingly broad range of slope forms including asymmetric degrading scarps and cinder cone profiles at low slope angles the dynamics are diffusion like with a short range thin tailed hop length distribution a parabolic convex upward equilibrium slope form and a linear relationship between transport rate and gradient as slope angle steepens the characteristic grain motion length scale begins to approach the length of the slope leading to planar equilibrium forms that show a strongly nonlinear correlation between transport rate and gradient these high probability long distance motions violate the locality assumption embedded in many common gradient based geomorphic transport laws the example of a degrading scarp illustrates the potential for grain motion dynamics to vary in space and time as topography evolves this characteristic renders models based on independent stationary statistics inapplicable an accompanying analytical framework based on treating grain motion as a survival process is briefly outlined

tidal cross strata and the sediment transport rate problem a geologist s approach abstract cross strata of large scale tidal ripples allow a detailed reconstruction of the kinematics of ripple migration they reflect tidal periodicities such as neap spring tide cycles or daily inequalities which can be used together with random thickness variations to study the sediment transport dynamics quantitatively as a function of the stream power since only a few current data are necessary the method is called the geologist s approach in this study the thickness of ancient some hundred years old tidal cross strata bundles is compared with the tidal range at neap and at spring the effect of randomly distributed current deviations due to wind driven current components is used as a control parameter sternberg s 1972 version of bagnold s sediment transport formula is shown to explain satisfactorily the cross strata structure even as high as several g cm sec this is more than one order of magnitude greater than the highest rates observed in the laboratory or in the field the only difference with sternberg concerns the limit of the exponential growth of bagnold s transport coefficient k

palaeoenvironment assessment of pliocene lom lignite bulgaria from bitumen analysis and preparative off line thermochemolysis abstract the dacian coal bearing province is located in nw bulgaria coal formation is thought to be connected with desiccation of the dacian basin during a prolonged regression in the late pontian and pliocene dacian romanian age a lom lignite sample was characterized via micropetrography bulk chemical analysis spectral methods and thermochemolysis the pollen record was poor suggesting coal formation under oxygen rich conditions during peatification straight chain alkanes alkan 2 ones alkanols des a triterpenoids aromatized triterpenoids aromatized hopane hopene hopanes and triterpenoids with a strong dominance of oleanane derived structures were present in the extracted bitumen the residue after extraction was subjected to preparative off line tetramethylammonium hydroxide tmah thermochemolysis the aliphatic products released were c22 c27 fatty acid fa methyl esters i e methoxymethyl esters c22 c28 even numbered diacids dimethyl esters with a smooth distribution and traces of i and ai c15 acid methyl esters trapped and bound fas were distinguished using tetraethylammonium acetate teaac treatment the main thermochemolysis products were phenols structurally related to lignin vanillyl and syringyl units were produced in similar amounts indicating nonwoody angiosperm vegetation as the main plant input to the palaeo swamp probably originating from marsh or grassland sources the bitumen provided unequivocal information for an angiosperm contribution to the mire while the results of the tmah pyrolysis revealed a concomitant angiosperm and gymnosperm input the biomarker assemblage makes the lom lignite unique in bulgaria all the other bulgarian neogene lignites being dominated by coniferous vegetation with only traces of angiosperm contributions

vascular plant biomarkers as proxies for palaeoflora and palaeoclimatic changes at the dogger malm transition of the paris basin france abstract vascular plant biomarkers are used here as a chemostratigraphic tool for tracing both palaeoflora and palaeoclimatic changes during the callovian and oxfordian in the paris basin the retene cadalene ratio shows low values in claystones from the middle callovian to the end of the lower oxfordian then increases drastically from the end of the lower oxfordian cordatum zone synchronously with the progressive development of the oxfordian carbonate platform the relative proportion of retene a conifer biomarker is strongly correlated with the abundance of some of its diagenetic precursors and with saturated diterpanes some of these are very common and abundant in the pinaceae family while specific markers for non pinaceae conifers are not detected thus the increase in the retene cadalene ratio around the cordatum zone reflects the rising proportion of pinaceae on the london brabant massif which was the nearest land from the locations studied as pinaceae show many morphological adaptations to dry climate compared to the other plants reported in the jurassic taphofloras of the paris basin their increasing proportion indicates an increasing aridity this climatic change is also supported by published geochemical palaeobiogeographical palynological palaeobotanical and mineralogical data a comparable increase in the relative proportion of retene was also described for the oxfordian of western australia which could be an argument for a worldwide increase in aridity at the end of the lower oxfordian

types of internal structure and external morphology of submarine dunes under the influence of tide and wind driven processes dover strait northern france abstract the expression of tide and wind driven processes in the internal architecture and external morphology of very large submarine dunes is investigated at a dune field located in the central part of the dover strait southern north sea current measurements and sediment transport calculations enable quantification of the dominant tide and wind driven processes and very high resolution seismic recordings are used to analyse internal structure and external morphology of dunes in the study area moderate to storm winds induce temporary currents that can lead to the reversal of sediment transport direction and induced erosive processes on the seabed dune master bedding consists of extended erosive surfaces with 9 11 slopes that bound storm generated sets of cross beds 1 5 4 85 m thick 2 65 m on average three types of architectures are observed within the dune field and occasionally within single dunes these types which display a strong linkage between internal structure and external morphology consist of 1 asymmetric dunes with cosets which dip in the direction of the marked external asymmetry of the dunes 2 dunes with a complex external morphology composed of mega herringbone structures each displaying an opposing progradation direction and 3 dunes with a symmetric megaripple bedding unit at their summit the diversity of the internal architecture and external morphology results from the variable combinations of tide and wind driven processes occurring in the study area the asymmetry of tidal peak current velocity and the relative strength of wind driven currents are the parameters that have the most important influence on dune architecture asymmetric dunes with cosets result from a strong asymmetry in tidal peak current velocity which is reversed only slightly during storms dunes with mega herringbone structures and dunes with symmetric megaripple units at their summit are observed in areas where the asymmetry of the tidal peak current velocity is negligible allowing reversal of the sediment transport and dune migration directions each time moderate winds blow the latter architectural type is specific to sand rich areas the different dune architecture types display strong geometrical similarities to structures observed in dunes from other shelf environments where driving processes are different this implies that a study based only on a geometric description of internal structures will not enable the reconstitution of ancient depositional environments a better discriminant criteria seems to be the thickness of the second order sets of cross beds which is correlated with specific hydro sedimentary processes dune height also probably has an important influence on the thickness of second order sets of cross beds as dune height and set thickness display a clear relationship in the present study

calibration and testing of upland hillslope evolution models in a dated landscape banco bonito new mexico 1 in this study we tested upland hillslope evolution models and constrained the rates of regolith production colluvial transport and eolian deposition over geologic time scales in a dated volcanic landscape in northern new mexico using field measurements of regolith thickness geochemical analyses of regolith bedrock and regional dust numerical modeling of regolith production and transport and quantitative analyses of airborne light detection and ranging lidar digital elevation models dems within this volcanic landscape many topographically closed basins exist as a result of compressional folding and explosion pitting during eruption the landscape has evolved from an initial state of no regolith cover at 40 5 ka to its modern state which has highly weathered regolith ranging from 0 to 3 m with local thickness values controlled primarily by topographic position our models constrain the maximum rate of regolith production in the study area to be in the range of 0 02 to 0 12 m kyr 1 and the rate of colluvial transport per unit slope gradient to be in the range of 0 2 to 2 7 m 2 kyr 1 with higher values in areas with more aboveground biomass we conclude that a depth dependent colluvial transport model better predicts the observed spatial distribution of regolith thickness compared to a model that has no depth dependence this study adds to the database of estimates for rates of regolith production and transport in the western united states and shows how dated landscapes can be used to improve our understanding of the coevolution of landscapes and regolith cover

the diagenetic fate of taraxer 14 ene and oleanene isomers abstract the extractable organic matter in holocene to early miocene deep sea sediments from site 645 odp leg 105 in baffin bay contains almost exclusively biological markers of terrigenous origin pentacyclic triterpenoids of the ursene and amyrin oleanene type often occur as the most abundant compounds in the aliphatic hydrocarbon ketone and alcohol fractions of the sediment extract a specific diagenetic reaction involves the conversion of taraxer 14 ene into olean 12 ene in the upper 700 metres of the sedimentary sequence the taraxerene to oleanene conversion is complete before the onset of isomerisation of diasterenes at c 20 in the sediment as well as in laboratory simulation experiments olean 12 ene further isomerises to olean 13 18 ene and olean 18 ene the latter of which may be the direct precursor of 18 h and 18 h oleanane found in sediments containing more mature organic matter and in crude oils the subsurface interconversion of these triterpenoid skeletons indicate that oleanane does not necessarily start life as an oleanoid

coevolution of nonlinear trends in vegetation soils and topography with elevation and slope aspect a case study in the sky islands of southern arizona 1 feedbacks among vegetation dynamics pedogenesis and topographic development affect the critical zone the living filter for earth s hydrologic biogeochemical and rock sediment cycles assessing the importance of such feedbacks which may be particularly pronounced in water limited systems remains a fundamental interdisciplinary challenge the sky islands of southern arizona offer an unusually well defined natural experiment involving such feedbacks because mean annual precipitation varies by a factor of five over distances of approximately 10 km in areas of similar rock type granite and tectonic history here we compile high resolution spatially distributed data for effective energy and mass transfer eemt the energy available to drive bedrock weathering above ground biomass soil thickness hillslope scale topographic relief and drainage density in two such mountain ranges santa catalina scm pinaleno pm strong correlations exist among vegetation soil topography variables which vary nonlinearly with elevation such that warm dry low elevation portions of these ranges are characterized by relatively low above ground biomass thin soils minimal soil organic matter steep slopes and high drainage densities conversely cooler wetter higher elevations have systematically higher biomass thicker organic rich soils gentler slopes and lower drainage densities to test if eco pedo geomorphic feedbacks drive this pattern we developed a landscape evolution model that couples pedogenesis and topographic development over geologic time scales with rates explicitly dependent on vegetation density the model self organizes into states similar to those observed in scm and pm our results highlight the potential importance of eco pedo geomorphic feedbacks mediated by soil thickness in water limited systems

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

biomarkers of holocene buried conifer logs from bella coola and north vancouver british columbia canada abstract the biomarker compositions of a holocene seep oil liquefied resin originating from a buried log of douglas fir pseudotsuga menziesii from bella coola bc canada and a holocene pine wood pinus sp sample from north vancouver bc canada were analyzed using gas chromatography mass spectrometry gc ms the total extract of the bella coola sample contains the sesquiterpenoid derivative calamenene and diterpenoids of the labdane abietane pimarane and phyllocladane classes a novel series of successively degraded labdane derivatives labdan 15 oic acid norlabdanoic acids drimenoic acid was detected in the polar fraction and a diagenetic pathway is proposed aromatic abietanes are the major components in the neutral fraction the neutral fraction of the pine wood contains two sesquiterpenoids calamenene cadalene diterpenoids of the abietane pimarane isopimarane and kaurane classes and a series of steroids 18 norabieta 8 11 13 triene dehydroabietin is the major component among the predominantly aromatic abietanes based on the compositions of the terpenoids it is concluded that the diagenesis of the pine and douglas fir logs probably occurred under anaerobic conditions leading to reductive reactions such as decarboxylation of resin acids with concurrent oxidation reactions to form the aromatic derivatives

hillslope evolution by nonlinear creep and landsliding an experimental study landscape evolution models are widely used to explore links between tectonics climate and hillslope morphology yet mecha nisms of hillslope erosion remain poorly understood here we use a laboratory hillslope of granular material to experimentally test how creep and landsliding contribute to hillslope erosion in our experimental hillslope disturbance driven sediment transport rates increase nonlinearly with slope due to dilation driven gran ular creep and become increasingly episodic at steep slope angles as creep gives way to periodic landsliding we use spectral analysis to quantify the variability of sediment flux and estimate the slope dependent transition from creep to landsliding the power spec trum of sediment flux steepens with hillslope gradient exhibiting fractal 1 f scaling just below the creep landsliding transition by evolving the experimental hillslope under fixed base level boundary conditions we demonstrate how disturbance driven transport gen erates hillslope convexity the transient evolution is consistent with numerical predictions derived from a recently proposed nonlinear transport model as initially steep hillslopes are lowered rapidly by landsliding before slopes decay slowly by creep dominated transport

estimates of sand transport in the oosterschelde tidal basin using current velocity measurements abstract estimates of sand transport have been made from mid depth velocity measurements in the oosterschelde tidal basin southwestern netherlands this involves 1 the use of a two region composite boundary layer model in deriving the local spatially averaged bed shear stress from velocity distributions over large bedforms megaripples and sandwaves the two regions are divided at 100 cm above the bed with an outer region roughness length of 1 5 cm and an inner region roughness length of 0 15 cm 2 the application of a modified bagnold s transport equation with the transport coefficient k depending on dimensionless excess shear stress in the form of a power law the calculations indicate very active sand movement in the present day oosterschelde tidal basin local sediment circulation may develop around shoals channel floor erosion may occur in parting areas of sediment transport the net sediment transport is mainly in the ebb direction estimates of sediment budget for the last 20 years show that large amounts of sand have been eroded from the oosterschelde tidal basin and transported to the ebb delta area these results are comparable with other estimates from echo sounding data reflecting the rapid adjustment of the basin to the increased tidal prism such active sediment redistribution and major morphological evolution processes would have important influence on the structural organization and sequential development of estuary ebb delta deposits information about the sedimentary processes in present day estuary tidal basins is valuable for a better understanding of ancient examples

the effects of bioturbation on soil processes and sediment transport abstract plants and animals exploit the soil for food and shelter and in the process affect it in many different ways for example uprooted trees may break up bedrock transport soil downslope increase the heterogeneity of soil respiration rates and inhibit soil horizonation in this contribution we review previously published papers that provide insights into the process of bioturbation we focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production using geometrical relationships and data from others work we derive simple sediment flux equations for tree throw and root growth and decay

bedload transport in two gravel bedded streams bedload transport measurements in two upland streams are considered as a function of the excess stream power exerted on the bed by the flow during low flows when the framework gravels remain undisturbed fine sediments are winnowed from the bed surface layer once a threshold of 3 4 w m 2 is exceeded and the transport rate is strongly supply limited however for stream powers in excess of 15 w m 2 framework gravels are mobilized and the efficiency of the transport process approaches a local maximum of about 1 per cent for discharges up to 2 3 of bankfull an inverse depth dependence in the efficiency of the transport process was noted but although bedload calibre increased as a function of discharge its influence on efficiency could not be demonstrated however it was suspected that the size sorting relationships of the bed material in a number of rivers in relation to the transport efficiency might profitably be examined further

responses of soil mantled hillslopes to transient channel incision rates 1 channel incision drives hillslope morphology in humid soil mantled landscapes when channel incision rates change numerous hillslope soil properties e g erosion rates soil thickness and soil production adjust in response to this change here we investigate the timescales of adjustment of hillslope soil properties when channel incision rates change in time an idealized soil mantled hillslope linear sediment flux law and soil density equal to bedrock density is investigated and the transient evolution of this hillslope is determined analytically this analysis reveals two dominant adjustment timescales the longer of these two timescales determines the rate at which the entire hillslope adjusts to a change in channel incision rates and is proportional to 4 2 2d where is the length of the hillslope and d is the sediment diffusivity numerical simulations are then used to examine responses of hillslopes that involve nonlinear behavior e g hillslopes that experience nonlinear sediment transport or have soil thicknesses that respond to the soil production function using these numerical models we show that the ratio between the soil density s and the density of the soil parent material can alter the long term response of the hillslope such that the characteristic timescale becomes 4 2 2d s in addition we show that the adjustments of the soil erosion rate the soil production rate and the soil thickness have different characteristic response timescales hillslopes that experience sediment flux that is proportional to the depth slope product respond on longer timescales than hillslopes that experience a linear sediment flux law when channel incision rates increase we illustrate how the spatial pattern of hillslope response to changes in channel incision rates can be used to constrain either channel incision histories or hillslope response timescales if the hillslope response timescale is known the pattern of hillslope disturbance can be used to constrain the celerity of a incision wave as it moves upstream through a channel if the channel incision history is known the hillslope response timescale may be evaluated on the basis of the spatial pattern of hillslope disturbance

saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast alaska abstract dinorlupanes norlupanes olean 12 ene 18 olean 12 ene and urs 12 ene occur in a heavily biodegraded tertiary oil tested from the ocs y 0849 1 well drilled on the hammerhead prospect in the beaufort sea offshore northeast alaska these indicators and other source related characteristics of the hammerhead oil ring a degraded oleanoids ursanoids and lupanoids v and ni less than 2 0 ppm v v ni less than 0 5 indicate a land plant angiospermous character in the source facies the olefins in the hammerhead and canadian oils are considered to be contributed directly from the source rather than extracted from adjacent immature non source sediments during migration as indicated by a the accompanying presence in the oil of saturated angiosperm markers and b the absence of measurable amounts of other olefins characteristic of immature organic matter e g diasterenes and hopenes

lithologic control on the form of soil mantled hillslopes slopes in steady state soil mantled landscapes tend to increase downslope in a way that balances local transport capacity with the sediment supplied from progressively larger source areas most formulations of sediment transport due to hillslope processes scale transport rate with local slope which produces convex up forms that are independent of the properties of the underlying lithologies in this study we document soil mantled hillslopes that show variations in slope that mimic the underlying stratigraphy we present stratigraphic and soil thickness measurements topographic analyses and numerical models to demonstrate that variations in rock type can impact the forms of these soil mantled hillslopes if hillslope transport rates scale with local slope and soil thickness this demonstrates that hillslope forms in soil mantled landscapes can be influenced by the underlying lithology through a coupling between the processes that produce soil from rock and those that transport this soil downslope

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

a sediment record of barrier estuary behaviour at the mesoscale interpreting high resolution particle size analysis abstract at present limited understanding of mesoscale years decades centuries back barrier lagoon barrier estuary behaviour is a critical shortcoming for resource managers and decision makers in this paper high resolution particle size analysis of a sediment core from an intermittently open and closed barrier estuary is utilised to reconstruct a history of back barrier environmental change at mesoscale temporal resolution sediments from pescadero marsh california were analysed for their particle size distribution at consecutive 2 mm intervals down core site selection informed by a time series of maps and aerial photographs coupled with a robust core chronology ensured that the particle size data primarily reflect changing hydrodynamics of the back barrier area over the european american era 1850 to the present following more traditional plotting of particle size data and summary statistics and statistical analysis of particle size end members visual analysis and categorisation of particle size distribution curves psdcs provide an effective basis for the identification of recurring modal sizes and subpopulations these particle size windows psws are interpreted as reflecting different modes of sediment transport and deposition i e suspension and saltation loads the varying prominence of which is interpreted as being modified by barrier integrity when considered together the down core mean particle size mps trend and individual psdcs offer considerable insight into mesoscale system behaviour at subannual resolution over multiple years this behaviour is expressed in the recurrence of characteristic barrier estuarine environments closed lagoon tidal lagoon tidal marsh and open estuary and the overall barrier regime and their persistence over the last c 150 years subannual and multiannual fluctuations in back barrier environmental configuration are seen to be superimposed on a longer term quasi stable barrier regime demonstrating the value of the applied methodology with regard to bridging the estuarine evolution long term stratigraphic and process short term geomorphic knowledge bases the documented behaviour suggests a level of innate morphological resilience in the system over the long term despite episodic disturbance by high energy storms such empirical demonstrations of resilient behaviour in coastal environments are rare at the mesoscale

nonlocal sediment transport on steep lateral moraines eastern sierra nevada california usa available for download is the author s version of the paper the final publisher s version is available at https dx doi org 10 1002 2017jf004325 the dataset doi is https doi org 10 15695 vudata cee 1

soil creep and convex upward velocity profiles theoretical and experimental investigation of disturbance driven sediment transport on hillslopes the movement of unconsolidated materials near the earth s surface is often driven by disturbances that occur at a range of spatial and temporal scales the nature of these disturbances ranges from highly variable such as tree turnover to periodic and predictable such as frost heave or creep to explore the effect of probabilistic disturbances on surface processes we formulated a granular creep model with analogy to rate process theory rpt used for chemical reactions according to the theory individual particles must be energized to a height greater than adjacent particles in order for grain dilation and transport to occur the height of neighbouring particles which is akin to activation energy in chemical reactions varies with slope angle such that energy barriers get smaller in the downslope direction as slopes steepen when slopes approach the friction limited angle of repose the height of energy barriers approaches zero and grains ow in the absence of disturbance an exponential function is used to describe the probability distribution of particle excitation height although alternative distributions are possible we tested model predictions of granular dynamics in an experimental sandpile in the sandpile acoustic energy serves as the disturbance agent such that grains dilate and shear in response particle velocities are controlled by the frequency of energy pulses that result in grain displacement using tracer particles we observed a convex upward velocity pro le near the surface of the sandpile consistent with predictions of our rpt based velocity model in addition we depth integrated the velocity model to predict how ux rates vary with inclination of the sandpile and observed non linear ux gradient curves consistent with model predictions by varying the acoustic energy level in the experimental sandpile we documented changes in the rate of grain movement similar changes in modelled velocities were achieved by varying the exponent of the particle excitation probability distribution the general agreement between observed and modelled granular behaviour in our simple laboratory sandpile supports the utility of rpt based methods for modelling transport processes e g soil creep frost heave and till deformation thus enabling us to account for the probabilistic nature of disturbances that liberate sediment in natural landscapes copyright 2004 john wiley sons ltd

preliminary study of the dynamic origin of the distribution pattern of bottom sediments on the continental shelves of the bohai sea yellow sea and east china sea the bottom sediment types in the bohai sea yellow sea and east china sea byecs are diversified and their distribution pattern is very complicated however the bottom sediment types can be simplified to be sandy sediment clayey sediment and mixed sediment which comprise the complicated distribution pattern of bottom sediment in the byecs the continental shelves of the byecs are broad with shallow water depths and tidal currents which are permanent and dominate the marine dynamics in the byecs based on numerical simulation of tidal elevations and currents in the byecs the rates of suspended load transport and bed load transport during a single tidal cycle for sediments of eight different grain size ranges are calculated the results show that any sediment whose threshold velocity is less than that of tidal current has the same transport trend suspended load transport rare bed load transport rate and the ratio of the former to the latter decrease with grain size becoming coarser and coarser the erosion accretion patterns of sediments with different grain sizes are determined by the sediment transport rate divergences and the results show that the patterns are the same for sediments with different grain sizes three main bottom sediment types i e sandy sediment mainly composed of fine sand clayey sediment mainly composed of silty clay and mixed sediment mainly composed of fine sand silt and clay are obtained by computation the three bottom sediment types and their distribution pattern are consistent not only with sediment transport field and the sea bed erosion accretion pattern obtained by simulation but also with field data of bottom sediment types and divisions in the byecs sand ridges form mainly in the areas with strong rectilinear tidal currents sand sheets form mainly in the areas dominated by strong rotatory tidal currents and clayey sediments i e mud patches form mainly in the areas with weak tidal currents hence not only the sandy sediments but also the clayey sediments in the byecs are formed under the control of the whole tidal current field of the byecs the three main bottom sediment types are not isolated respectively in fact they constitute a whole tidal depositional system under the condition with no cyclonic cold eddy the clayey sediments in the byecs can form in weak tidal current environments therefore a cold eddy is not necessary for the deposition of clayey sediments in the byecs c 2000 academic press

stability of creeping soil and implications for hillslope evolution the geomorphic behavior of a soil mantled hillslope undergoing diffusive creep involves a coupling between changes in land surface elevation soil transport rates soil production and soil thickness a linear stability analysis suggests that the coupled response of the soil mantle to small perturbations in soil thickness or surface topography is influenced by two factors the diffusive like behavior of soil creep has a stabilizing effect wherein perturbations in land surface elevation are damped the relation between the soil production rate and soil thickness may be either stabilizing or destabilizing a monotonically decreasing production rate with soil thickness reinforces the stabilizing effect of diffusive land surface smoothing an increasing production rate with soil thickness has a destabilizing effect wherein perturbations in soil thickness or the soil bedrock interface are amplified despite the presence of diffusive land surface smoothing this coupled behavior is insensitive to the transport relation whether the soil flux is proportional to the land surface gradient or to the product of the soil thickness and land surface gradient the latter type of relation nonetheless could lead to a more complex hillslope form than might otherwise be expected for purely diffusive transport moreover the response to periodic sinusoidal variations in the rate of stream downcutting at the lower hillslope boundary involves upslope propagation of coupled damped waveforms in the land surface and the soil bedrock interface the distance of upslope propagation goes with the square root of the product of the transport diffusion like coefficient and the period of the downcutting rate the upper part of the hillslope is therefore insensitive to relatively high frequency variations in stream downcutting so together with a stable behavior of the coupled soil mantle bedrock system this part of the hillslope may exhibit a tendency toward uniform lowering while the lower part behaves transiently conversely in the presence of low frequency variations in stream downcutting hillslope morphology and soil thickness variations are more likely to reflect unsteady conditions over the entirety of the hillslope

maceral composition and molecular markers of two condensed middle holocene peat profiles in n spain abstract this study deals with the palaeohydrological information obtained from lipids composition and vegetal tissue preservation of two peat cores from asturias north spain the two profiles differ in the type of peatland raised bog in la borbolla and blanket bog in buelna and the type of organic matter being more bryophytic in the raised bog and more herbaceous in the blanket bog the peatlands are located close to the coast on impermeable old flat erosion surfaces which favoured peat accumulation within a distance of 3 5 km from each other the accumulation rate varied between 0 05 and 0 07 mm yr and the records extend from around 9000 to 2500 cal yr bp the main differences between the two peat sites can be summarized as follows the raised bog has lower mineral matter content and h c atomic ratio and higher c n ratio and extraction yields compared to the blanket bog it has also a higher tissue preservation index for huminite macerals and increasing inertodetrinite index with depth regarding biomarkers the raised bog has a relatively higher concentration of n alkane 2 ones compared to the corresponding n alkane of similar carbon number higher concentration of medium vs high molecular weight methyl ketones and higher triterpenoids steroids ratio than the blanket bog alternating humid dry periods have been recorded in both profiles based on lipid concentrations indicating that the sphagnum rich intervals in the raised bog are more sensitive than the herbaceous blanket peat record to climatic variations the main humid intervals identified are dated as 5000 7500 cal yr bp in the blanket bog and as 6000 3500 cal yr bp and last 2500 cal yr bp in the raised bog and correlate with the humid periods traced in other peatlands locations in this region the transition middle to late holocene is characterized by humid conditions in the region which favoured the sphagnum growth in the peats the reflectance of huminite in these records appears to be more related with differences in the oxidative conditions than with variation of peat maturity it is higher in the layers with high mineral matter content at the beginning of organic matter accumulation and also in the upper part of the profile subjected to seasonal desiccation a more intense biochemical gelification coincides with higher concentration of hopanoids derived from bacteria in the upper part of the profile acrotelm high amount of nonadecan 2 one k 19 and high concentrations of triterpenyl acetates which are also determined in other peat profiles from northern spain are also detected in these profiles this indicates that the specific conditions required for the formation of these compounds probably associated to wet temperate climate dominated throughout the region

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient