subtidal occurrences of ladder back ripples their significance in palaeo environmental reconstruction ladder back ripples are common on modern intertidal flats and have been thought to be diagnostic of deposition in this environment recognition of superimposed asymmetric ladder back ripples in a subtidal back barrier estuary and superimposed symmetric ladder back ripples in an embayed shallow marine environment indicates that these features are not diagnostic of deposition in the intertidal zone only but can occur in other depositional environments produced by different mechanisms and on different scales the presence of ladder back ripples in the subtidal zones challenges aspects of a model used to determine the palaeotidal range of ancient tidal sequences

how do pediments form a numerical modeling investigation with comparison to pediments in southern arizona usa pediments are gently sloping low relief bedrock erosional surfaces at the bases of mountain ranges pediments tend to form more readily in arid climates and in weathering resistant lithologies but the processes responsible for pediment formation are still not widely understood after more than a century of debate in this paper i investigate the behavior of a coupled numerical model for the evolution of mountain ranges and their adjacent piedmonts that includes bedrock erosion in channels soil production and erosion on hillslopes and the fl exural isostatic response of the lithosphere to erosional unloading for relatively small values of the fl exural parameter erosion of the mountain range leads to suffi cient fl exural isostatic tilting of the adjacent piedmont that a suballuvial bedrock bench is exhumed to form an erosional surface on the piedmont in addition slope retreat at the mountain front and subsequent tilting of the abandoned surface can contribute to pediment formation by lengthening the pediment in the upslope direction the rate of erosion on the piedmont must also be greater than or equal to the rate of soil production thereby creating an erosional surface that has at most a thin veneer of soil or regolith the rate of soil production depends primarily on climate and lithology with lower soil production rates associated with more arid climates and more resistant lithologies the model predictions are compared to morphometric analyses of pediments in the southwestern united states and to the detailed morphology of two classic pediments in southern arizona

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

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

a rudimentary mechanistic model for soil production and landscape development a rudimentary mechanistic model for soil production and landscape development is proposed the continuity equation of the model assumes that the change in soil thickness over time depends on the production of soil from the weathering of bedrock and the transport of soil through natural surface erosion the parameters for the model include the weathering rate and erosive diffusivity weathering rate is expressed as an exponential decay function of soil thickness which represents mechanical weathering erosive diffusivity can be estimated from soil erosion models the model is solved numerically using the finite difference approach and is applied to a numerical example simulation is performed for a hypothetical landscape with a series of hills and valleys results show the development rate of soil initially is very large and slows down until it reaches a steady state defined by a constant change in soil thickness the model also exhibits the characteristics of a nonlinear dynamic system nonlinearity of soil thickness and curvature and initial randomness appears to cause chaos instability in the system the results show promising progress in quantitative modelling of pedogenesis the limitations and suggested improvements of the model are also presented

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

linking soil element mass transfer to microscale mineral weathering across a semiarid environmental gradient abstract understanding controls on silicate weathering is critical to characterizing critical zone evolution the objective of this study was to investigate how climate vegetation and landscape position control feldspar transformations across a semiarid environmental gradient granitic surface soil and saprock samples were collected from desert scrub and mixed conifer sites within the santa catalina mountain critical zone observatory where mean annual temperature ranges from 24 c to 10 c and mean annual precipitation from 25 to 85 cm quantitative x ray diffraction x ray fluorescence and electron microprobe analyses were employed to quantify elemental changes in bulk soils and across plagioclase grains the chemical depletion of na in bulk soils ranged from 5 4 15 in the desert scrub sites relative to 16 33 in the mixed conifer sites plagioclase grain alteration was classified into unaltered edge and altered sections to compare microscale weathering and elemental variation the na al and si al ratios decreased from unaltered to edge to altered grain sections in the mixed conifer sites whereas the element ratios of the desert scrub system were similar between unaltered and edge grain sections and only exhibited significant decreases in na al and si al ratios between edge and altered materials the microscale depletion of na and si suggested increased silicate weathering in the cooler wetter and more biologically productive mixed conifer system compared to the hot dry desert scrub system the results also demonstrated a topographic control on mineral transformation where increased plagioclase weathering occurred in convergent footslope landscapes with little change in elemental depletion of soils in divergent summit sites

sedimentary facies of the eastern pacific s northernmost reef like setting cabo pulmo mexico abstract cabo pulmo mexico is often cited as the eastern pacific s northernmost coral reef we investigated sedimentary dynamics to verify whether the system functions sedimentologically as a reef which would mean that it retained internal sediment in a framework and exported peri reefal sediment creating clearly identifiable facies dominated by reefal fauna we mapped distribution of sediments using grab samples the acoustic ground discrimination systems qtc view and echo plus at 50 khz signal frequency and an ikonos satellite image morphologically the bay of cabo pulmo can be divided into intrusive dikes and rocky hardgrounds in less than 10 m depth and a sandy interior with rocky outcrops sloping to over 40 m reefal fauna without lasting framework building but with production of typically reef associated carbonate sediments as well as a patch reef facies were found on the dikes and hardgrounds sediments in the bay were a mixture of carbonates and siliciclastics and were influenced by a seasonal river near the bay s center that imported siliciclastic material to the north and south sediments had a higher carbonate content although overall the bay was characterized by 50 siliciclastics the shallower subtidal sands were dominated by mollusk fragments whereas in depths 30 m planktonic foraminiferal sand was found acoustically and optically remote sensed maps were used to differentiate between the rocky and sandy areas and to identify the presumed off shelf transport pathway of reef derived carbonates overall the sedimentary system is characterized by carbonate production but the coarser reef derived carbonates coral and reef dwelling mollusks are transported off shelf along a steep depth gradient and little typical peri reef sediment remains this transport is likely aided by storms since no sediment retaining frameworks are formed the dikes cannot retain internal sediment and the reefal fauna was not dominant in sediments throughout the bay we conclude that cabo pulmo sedimentologically functions only in a limited way like a coral reef

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

isotopic composition of old ground water from lake agassiz implications for late pleistocene climate a uniform oxygen isotope value of 25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial lake agassiz basin the lake occupied parts of north dakota and southern manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of canada ground water from thick late pleistocene age clay deposits elsewhere a till in southern saskatchewan and a glaciolacustrine deposit in northern ontario show the same value at similar depths these sites are at about 50 n latitude span a distance of 2000 kilometers and like the lake agassiz sites have a ground water velocity of less than a few millimeters per year the value of 25 per mil is characteristic of meltwater impounded in the southern basin of lake agassiz this value corresponds to an estimated air temperature of 16 c compared with the modern temperature of 0 c for this area

the implications of geology soils and vegetation on landscape morphology inferences from semi arid basins with complex vegetation patterns in central new mexico usa abstract this paper examines the relationship between land surface properties e g soil vegetation and lithology and landscape morphology quantified by the catchment descriptors the slope area s a relation curvature area c a relation and the cumulative area distribution cad in two semi arid basins in central new mexico the first site is composed of several basins located in today s desert elevations with mesic north facing and xeric south facing hillslopes underlain by different lithological formations the second site is a mountainous basin exhibiting vegetation gradients from shrublands in the lower elevations to grasslands and forests at higher elevations all three land surface properties were found to have significant influences on the s a and c a relations while the power law exponents of the cads for these properties did not show any significant deviations from the narrow range of universal scaling exponents reported in the literature among the three different surface properties we investigated vegetation had the most profound impact on the catchment descriptors in the s a diagrams of the aspect controlled ecosystems we found steeper slopes in north facing aspects than south facing aspects for a given drainage area in elevation controlled ecosystems forested landscapes exhibited the steepest slopes for the range of drainage areas examined followed by shrublands and grasslands in all soil textures and lithologies in the c a diagrams steeper slopes led to a higher degree of divergence on hillslopes and a higher degree of convergence in the valleys than shallower slopes the influence of functional types of vegetation detected on observed topography provided some initial understanding of the potential impacts of life on the organization of topography this finding also emphasizes the critical role of climate in catchment development we suggest that climatic fluctuations that are capable of replacing vegetation communities could lead to highly amplified hydrological and geomorphic responses

shoreline deposits and diagenesis resulting from two late pleistocene highstands near 5 and 6 metres durban south africa in exposures of pleistocene rocks on the east coast of south africa eight sedimentary facies were distinguished on the basis of petrology grain size internal structures and field relationships these are interpreted as deposits of surf zone breaker zone swash zone backbeach boulder beach and dune environments three phases of deposition and diagenesis are recognized as a result of the stabilising effect of pre existing coastal facies the deposits from successive sea level stands are stacked vertically in a narrow coast normal strip early cementation prevented erosion of the deposits during subsequent transgressions deposition of subsequent facies took place on an existing coastal dune facies 1 a terrace was cut into this dune at a sea level 4 5 to 5 m above present at this sea level clastic shoreline sediments were deposited which make up the main sedimentary sequence exposed facies 2 7 the steep swash zone coarse grain size and comparison with modern conditions in the study area indicate clastic deposition on a high energy wave dominated microtidal coastline vertical stacking of progressively shallower water facies indicates progradation associated with slightly regressive conditions prior to stranding of the succession above sea level during a subsequent transgression to 5 5 or 6 m above present sea level a second terrace was cut across the existing facies which by then were partly lithified a boulder beach facies 8 deposited on this terrace is indicative of high wave energy and a rocky coastline formed by existing cemented coastal facies comparison with dated deposits from other parts of the south african coast suggest a late pleistocene age for facies 2 8 deposition was terminated by subsequent regression and continuing low sea levels during the remainder of the pleistocene cementation of the facies took place almost entirely by carbonate precipitation the presence of isopachous fibrous cements suggests early cementation of facies 1 2 3 and 4 under marine conditions initially as aragonite which has since inverted to calcite facies 5 6 and 7 are cemented only by equant calcite spar evidence of cementation in the meteoric phreatic and vadose zones lowering of the water table during regression caused the remaining pore space in facies 1 2 3 and 4 to be filled with equant calcite spar decementation in a 130 cm wide zone is attributed to water table shifts associated with the later transgression which deposited facies 8 the vertical stacking of the two depositional sequences may be attributed to rapid cementation of facies 2 3 4 5 6 and 7 under humid subtropical conditions this lithified sequence then acted as a focus for deposition of coarse grained shoreline facies facies 8 during the subsequent transgression

geomorphic response to seasonal variations in rainfall in the southwest united states the interaction of the north american monsoon with watershed hydrology and landscape response is evaluated by observing geomorphic characteristics of hillslopes hydrology and stream channels in two mountain ranges with contrasting intensity of precipitation the study compares watersheds in the hualapai and santa catalina mountains in arizona which are similar in lithology elevation tectonic setting vegetation and annual precipitation but differ in the proportion of precipitation received in summer thunderstorms the hualapai mountains receive most of their precipitation in winter whereas rainfall in the santa catalina mountains occurs mostly in summer drainages in the santa catalinas are more variable in local relief and exhibit much more exposed bedrock and higher drainage density the trunk channel of a major drainage in the santa catalina mountains has measured discharges several orders of magnitude greater than a channel draining a comparable area in the hualapai mountains the alluvial segment of the channel in the santa catalina piedmont additionally displays greater concavity smaller width to depth ratios and a larger caliber of bed material in contrast to conventional interpretation summer monsoonal precipitation is not primarily responsible for generating most of the discharges that modify channels in large scale drainages in the monsoonal climate regime of the santa catalinas small basins flood most often in summer whereas larger drainages exhibit peak discharges in response to low intensity winter precipitation we attribute the paradoxical discharge response of larger drainages to the small spatial scale of summer thunderstorms which fail to deliver enough precipitation to generate floods in these larger basins but do prime hillslopes by stripping colluvium and lowering hillslope infiltration rates making the large drainages more responsive to areally extensive winter storms

solute transport in formations of very low permeability profiles of stable isotope and dissolved noble gas contents of pore water in the opalinus clay mont terri switzerland pore water profiles of water stable isotope and dissolved noble gas content have been determined across the opalinus clay and adjacent formations at the rock laboratory at mont terri we have found enhanced helium contents up to 4he 1 10 4 cubic centimeters at standard pressure and temperature per gram of pore water and argon isotope ratios 40ar 36ar ratios up to 334 due to accumulation of 4he and 40ar produced in situ the helium profile was found to be in steady state with respect to in situ production and diffusive loss into the adjacent limestones where groundwater circulates from this profile a representative mean value of the apparent diffusion coefficient for helium in the pore water of the whole formation was derived for the first time to be da 3 5 10 11 m2 s 1 which is more than two orders of magnitude lower than the diffusion coefficient d0 in free water the stable isotope profile however indicates a component of fossil marine pore water which has not yet been replaced by molecular diffusion of meteoric water from the adjacent limestone and shale formations over the past 10 million years

veins in clay rich aquitards as records of deformation and fluid flow events in northern switzerland abstract the jurassic clay rich aquitard sequence underlying the swiss molasse basin is locally penetrated by unusually frequent veins consisting of calcite celestite in particular in the schlattingen 1 and oftringen drill cores the veins are linked to extensional brittle structures with shear senses ranging between dip slip and strike slip deformation triggered transient and localised events of fluid flow within the aquitard followed by sealing of the structures by the vein minerals vein calcite was dated by la icp ms analysis using the u pb method while this was a demanding undertaking given the low u and high common pb contents of calcite 9 significant ages could be obtained two groups of ages can be distinguished namely 31 39 and 11 18 ma both age groups are consistent with the known regional tectonic evolution the older age group corresponds to the main phase of rifting in the upper rhine graben a major crustal discontinuity whose effects were not limited to the graben proper but affected large parts of the molasse basin the younger age group is linked to crustal tilting and related extensional deformation isotopic compositions of o and c in vein calcite from the schlattingen 1 core show substantial variability but do not discriminate between veins of the two age groups in contrast 87sr 86sr ratios in veins show different signatures the depth trend of 87sr 86sr ratios in veins fits well with that in pore water obtained by rock squeezing the two data sets define a trend of values increasing with depth connecting the current values in the embedding malm and keuper aquifer waters this trend is best explained as a near steady state diffusion profile while advective mixing of waters originating from the embedding aquifers to produce the veins implying structures that cross cut the whole low permeability sequence cannot be discarded on the basis of existing data it is considered more likely that the veins have local fluid sources these are mixtures of local pore water with a possible contribution of water from the nearest aquifer implying maximum vertical advection distances in the order of 50 100 m

use of vertical profiles of δ18o to constrain estimates of hydraulic conductivity in a thick unfractured aquitard vertical distributions of 18o were used to constrain hydraulic conductivity k in a thick unfractured aquitard previous investigations utilizing permeability tests at a variety of scales keller et al 1989 indicated that bulk k at the site ranges from 3 5 0 11 m s to 1 2 10 10 m s advective displacements calculated on the basis of these k values lead to a wide range of predicted distributions of natural tracers after 11 000 years comparison of 18o distributions and simulated advection diffusion profiles provide a more precise constraint on advective displacement and hence on k the simulations cast in terms of a peclet number p v2t d ranging in value from 0 to 12 indicate that transport is diffusion controlled and that k is actually less than 1 2 10 11 m s p greater than 0 1 k 1 2 10 11 m s overestimates transport this result indicates that conventional permeability tests in very tight media tend to overestimate k in practical terms advective transport at the site is negligible and transport can be simulated with diffusion only p o

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

the origin and timing of multiphase cementation in carbonates impact of regional scale geodynamic events on the middle jurassic limestones diagenesis paris basin france the middle jurassic carbonates of the eastern part of the paris basin display surprisingly low values of porosity and permeability 15 and k 0 5 md the main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs a fate that did not befall their equivalents in deeper central parts of the paris basin using petrographic and geochemical analyses stable o and c isotopes sr isotopes major elements we identify six calcitic spar stages two dolomite stages and several episodes of fracturing and stylolitization ordered in paragenetic sequence cement quantification shows the predominance of two blocky calcite cement stages 75 of total cementation o and sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped jurassic seawater and meteoric water or from buffered meteoric waters in the geological history of the paris basin major meteoric water inputs were possible during the early cretaceous when the middle jurassic carbonates cropped out at its northern and eastern borders lateral meteoric recharge may have occurred as a result of two separate uplift events late cimmerian unconformity and late aptian unconformity and the related exposures of carbonates to the north of the study area this palaeohydrological circulation brought about a significant reduction of porosity from 40 to 10 through calcite cement precipitation the early cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the london brabant massif across all of northwestern europe a subsequent dolomite and calcite cementation stage accounts for about 5 of the total cement volumes this late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the late oligocene extension episode

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

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

the occurrence and formation of ladderback ripples in subtidal shallow marine sands zululand south africa abstract until recently ladderback ripples have been considered diagnostic of late stage emergence run off in intertidal environments observations have demonstrated that ladderback ripples may also occur in the subtidal environment new underwater observations off the zululand coast support reddering s assertion that ladderback ripples are not confined to tide dominated environments two types of ladderback ripple are described they form in shallow submarine bioclastic and terrigenous sediments on the landward margin of offshore coral reefs the main ripple set in each instance is oriented sub parallel to the shoreline and is produced by the dominant southeasterly swell while superimposed ripple sets in the troughs of the larger sets are formed by two mechanisms 1 the approach of low amplitude high frequency northeasterly to easterly swells which are not sufficiently strong to change the orientation of the dominant larger set and 2 longshore currents produced by oblique wind driven swells in small coastal embayments when conditions change the superimposed ripples are rapidly reworked and incorporated into the main ripple set they therefore have a low preservation potential both the occurrences documented here and those reported previously are in microtidal wave dominated settings

detailed mapping of shallow landslides in eastern oklahoma and western arkansas and potential triggering by oklahoma earthquakes abstract landslides have long been considered one of the main erosive drivers that sculpt hillslopes over time tectonic forces raise slopes that can be sculpted by climate and the degree to which they can be sculpted depends upon the underlying lithology and hillslope geomorphology landslides destroy life and property and contribute to the evolution of mountain landscapes by generating and transporting hillslope sediments in this study we investigate the dynamics of soil mantled hillslopes in eastern oklahoma and western arkansas usa by mapping shallow landslides evaluating the frequency and magnitude of the landslides and quantifying the surface geometries we mapped 185 shallow landslides in a 150 km2 area the approximate ages of landslides and the frequencies and magnitudes area volume and runout were estimated using historical aerial photographs the landslide database was then used to compute rate of landslide occurrence and sediment yield in addition landslide surface geometries including slope curvature and surface roughness were determined from 10 m ned and 2 m lidar elevation data the hillslope susceptibility studies derived from elevation data were augmented by our review of common historical accounts that link landslides in the study region to the 1952 m 5 4 el reno oklahoma earthquake 300 km away in light of that case study we determined the frequency of historical earthquakes that impart 2 kpa dynamic stresses for the study area since 1900 and find an increased potential for dynamic stress perturbation of landslide activity since 2010 all these characteristics were then evaluated to understand the dynamics of hillslopes and hillslope susceptibility to shallow landslides frequency assessment of mapped landslides suggested that frequency of landslides increased significantly during 2005 2016 compared to 1995 2005 on average 10 shallow landslides occurred every year during 2005 2016 these landslides alone contributed 1 5 105 m3 yr sediment yield rate 0 10 cm yr of sediments surface roughness values were relatively higher in landslide areas compared to that of surrounding non landslide areas the surface roughness index mapped 84 of observed landslides and suggests that the index could be used to map hillslope susceptibility to landslides for future planned studies

origin of the oil field brines in the paris basin from br sup minus cl sup minus ratios coupled with stable isotope compositions the components of deep sedimentary brines namely primary and secondary brines from dissolving evaporites and diluting waters of meteoric origin can be identified and in favorable cases their respective proportions can be quantified dilution of primary marine brines mother liquors of halite by meteoric waters has occurred in the dogger and the keuper aquifers the presence of highly saline brines molality of cl sup minus 3 9 in the rhaetian aquifer may be due to dissolution of primary marine halite by sea water with minor contributions of primary brines the resulting mixture is diluted by meteoric circulation

stable isotope conservation and origin of saline waters from the middle jurassic aquifer of the paris basin france abstract seventy nine samples of formation water from geothermal boreholes oil field and ground water wells tapping the dogger middle jurassic limestone reservoir of the paris basin have been analyzed for their 2h 18o tds bromide and chloride contents geostatistical mapping of 2h and of 18o contents and their variations with chloride content indicate that both isotopes have a common origin and a similar behaviour within the aquifer the 2h and 18o values increase progressively from the outcrops toward a zone where temperature cl and tds values are high the 2h and 18o values are very uniform in this zone and do not show any relation with formation temperature in contrast to what is generally observed in other sedimentary basins a discussion of isotopes exchange with the carbonate matrix for oxygen and with h2s for deuterium shows that such processes are not controlling the heavy isotope contents of groundwaters this is attributed to the relatively short residence time of groundwaters in the aquifer both 2h and 18o contents of groundwater may thus be considered as conservative tracers in the dogger aquifer of the paris basin and their initial contents are modified only by fluid mixings complex mixing processes account for stable isotope composition tds cl and br values of the dogger fluids all mixtures include a brine component meteoric water percolated and dissolved halite in the triassic aquifer secondary brine this saline solution mixed with some residual primary brine then migrated via vertical faults into the dogger aquifer such migration is found to be in agreement with data from fluid inclusions in late carbonate cements from the liassic and dogger strata the requirement that these units were exposed implies that meteoric invasion could not have occurred before the tertiary successive mixings of the brine with several types of meteoric waters depleted in heavy isotopes account for the present isotope and chemical compositions of the dogger fluids

stable water isotopes in pore water of jurassic argillaceous rocks as tracers for solute transport over large spatial and temporal scales 1 in order to characterize the large scale transport properties of the opalinus clay formation the pore water isotope composition 18o and 2h was determined on samples from the deep borehole benken northeastern switzerland across jurassic argillaceous rocks the sequence of claystones and marls delimited by two aquifers is located at depth from about 400 to 700 m and exhibits very low hydraulic conductivities below 10 13 m s 1 the isotope data of the pore water were obtained from core samples by diffusive vapor equilibration vacuum distillation and squeezing compared with the other methods vacuum distillation led to too low values to evaluate the large scale transport properties of the formation we performed a series of advective dispersive model calculations and compared them with the experimental data in accordance with the hydrogeological history we varied initial and boundary conditions as well as model parameters the main results can be summarized as follows 1 molecular diffusion to the underlying aquifer can explain the general features of the isotope profiles 2 no signatures of advective flow could be detected 3 the evolution time is of the order of 0 5 1 ma relying on laboratory diffusion coefficients with a possible range of about 0 2 2 ma which is geologically plausible and 4 parameters measured on small scales centimeters or meters and months are also plausible at the formation scale tens of meters and millions of years for the sediments investigated

the humped soil production function eroding arnhem land australia we report erosion rates and processes determined from in situ produced beryllium 10 10be and aluminum 26 26al across a soil mantled landscape of arnhem land northern australia soil production rates peak under a soil thickness of about 35 cm and we observe no soil thicknesses between exposed bedrock and this thickness these results thus quantify a well defined humped soil production function in contrast to functions reported for other landscapes we compare this function to a previously reported exponential decline of soil production rates with increasing soil thickness across the passive margin exposed in the bega valley south eastern australia and found remarkable similarities in rates the critical difference in this work was that the arnhem land landscapes were either bedrock or mantled with soils greater than about 35 cm deep with peak soil production rates of about 20 m ma under 35 40 cm of soil thus supporting previous theory and modeling results for a humped soil production function we also show how coupling point specific with catchment averaged erosion rate measurements lead to a better understanding of landscape denudation specifically we report a nested sampling scheme where we quantify average erosion rates from the first order upland catchments to the main sixth order channel of tin camp creek the low 5 m ma rates from the main channel sediments reflect contributions from the slowly eroding stony highlands while the channels draining our study area reflect local soil production rates 10 m ma off the rocky ridge 20 m ma from the soil mantled regions quantifying such rates and processes help determine spatial variations of soil thickness as well as helping to predict the sustainability of the earth s soil resource under different erosional regimes copyright 2009 john wiley sons ltd

marine geology of the sodwana bay shelf southeast africa abstract the geostrophic current controlled northern zululand shelf displays a unique assemblage of interesting physical sedimentological and biological phenomena the shelf in this area is extremely narrow 3 km and is characterised by submarine canyons coral reefs and steep gradients on the continental slope three submarine canyons occur in the study area and are classified as mature or youthful phase canyons depending on the degree to which they breach the shelf these canyons originated as mass wasting features which were exploited by palaeo drainage during sea level regressions shelf lithology is dominated by a series of coast parallel patch coral reefs which have colonised beachrock and aeolianite sequences that extend semi continuously from 5 to 95 m and delineate late pleistocene palaeocoastline events the unconsolidated sediment on the shelf is either shelf sand mainly terrigenous quartz grains or bioclastic sediment large scale subaqueous dunes commonly form in the unconsolidated sediment on the outer shelf due to the agulhas current flow these dunes occur as two distinct fields at depths of 35 to 70 m the major sediment transport direction is towards the south but occasional bedload parting zones exist where the bedform migration direction changes from south to north

identifying temporally and spatially changing boundary conditions at an aquifer aquitard interface using helium in porewater abstract helium concentrations and 3he 4he isotope ratios of porewater groundwater and rock were measured on samples collected from a jurassic sediment sequence at the mont terri underground rock laboratory northern switzerland porewater he data of rock samples collected from borehole bdb 1 at high spatial resolution across a karstic limestone unit passwang formation into the underlying claystone sequence opalinus clay staffelegg formation describe a continuous profile from the water conducting zone in the limestone into the clay rich rocks of low permeability concentrations of 4he 3he and their parent nuclides in the rock allow calculating in situ production and accumulation terms since the time of sedimentation 90 97 of the in situ produced 4he has been released to the porewater today only 2 5 of the maximum possible accumulated 4he is still retained in the porewater while the major part of in situ produced 4he was removed from the system presumably by porewater groundwater exchange the porewater 4he concentrations show a diffusion profile from the aquitard towards the aquifer reflecting a a transient state between 4he in situ production and porewater groundwater exchange b a transient state from previously higher 4he concentrations in the porewater and c a spatially variable boundary in the karstic limestone unit evolutionary models of porewater 4he concentration profiles in combination with constraints from independent chemical and isotopic tracers allow deciphering a complex palaeo hydrogeological history of the system over about the last 30 ka a local excursion from the general profile towards higher 4he concentrations and 3he 4he ratio in a limestone layer in the opalinus clay cannot be further constrained in time based on the present sample frequency but appears to represent a hydrogeological signal

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

fault and fault rock characteristics associated with cenozoic extension and core complex evolution in the catalina rincon region southeastern arizona cenozoic extensional deformation in southern arizona included 1 a neogene phase of basin and range deformation recorded by high angle normal faults and 2 an earlier phase of detachment faulting and brittle ductile crustal shearing associated with tectonic denudation of metamorphic core complexes in the catalina rincon region exposed fault zones produced at different crustal depths during successive extensional episodes display differing fault geometries and types of fault rocks formed during progressive crustal extension detachment faults are associated with both mylonites produced by ductile shear and cataclasites produced by brittle shear younger faults formed at shallower depths are associated with less intense cataclastic deformation and with brittle fracturing that includes transtensile phenomena at the shallowest crustal levels represented qualitative measures of net displacement along individual fault zones are provided by 1 the nature of contrasts among successively overprinted fabrics and internal structures in the footwall and 2 the degree of contrast between fabrics and structures of footwall and hanging wall rocks footwalls of the oldest structures display varied brittle overprints of ductile fabrics and are juxtaposed across gouge zones along detachment surfaces with stratal successions cut by multiple brittle shear surfaces footwalls of younger structures formed at shallower depths display multiple generations of cataclastic features including brecciation of variable intensity and cataclasite dikes but are juxtaposed against hanging wall strata that are only moderately deformed by subsidiary faults the shallowest fault zones lack either structural overprints in their footwalls or any significant contrasts between footwall and hanging wall deformation exposures of mid crustal rocks within the core complexes reflect successive exhumation and uplift of fault footwalls during sequential episodes of deformation the present high elevation of mylonitic rocks in the catalina rincon metamorphic core complex reflects dip slip and isostatic footwall flexure during basin and range deformation as well as tectonic denudation during detachment faulting net uplift of core rocks resulted from multiple phases of deformation

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

long term biogenic soil mixing and transport in a hilly loess mantled landscape blue mountains of southeastern washington article i nfo in soil mantled landscapes downslope sediment transport occurs via disturbance driven processes that vary with climate and vegetation change to help constrain the long term 10 yr pattern and rate of soil mixing and transport in forests we analyzed the distribution of tephra grains in soil along a hillslope transect in the blue mountains se washington deposited within a loess mantle tephra associated with mt mazama 7 7 cal kyr b p serves as a marker bed for estimating erosion and transport rates moving downslope the buried tephra horizon is progressively exhumed and becomes increasingly mixed in the upper soil layer reflecting disturbance and transport via tree root growth and turnover this pattern also implies increasing erosion rates downslope and our hillslope transect becomes increasingly convex coincident with progressive exhumation of the tephra layer this systematic correspondence between topographic form specifically local convexity and surface lowering is consistent with theoretical models for which soil transport rates depend on slope inclination from our analysis calibrated coefficients for a linear slope dependent transport model are on the order of 10 3 m 2 yr 1 consistent with previous work in forested loess mantled landscapes in addition our results reveal both the high degree of soil mixing over millennial timescales and the local variability of mixing in forested landscapes furthermore the results enable us to quantify the amount of energy expended by trees in mixing and transporting soil and the net sediment transport fraction of the net primary productivity npp of the ecosystem published by elsevier b v

vegetation modulated landscape evolution effects of vegetation on landscape processes drainage density and topography 1 topography acts as a template for numerous landscape processes that include hydrologic ecologic and biologic phenomena these processes not only interact with each other but also contribute to shaping the landscape as they influence geomorphic processes we have investigated the effects of vegetation on thresholds for channel initiation and landform evolution using both analytical and numerical approaches vegetation is assumed to form a uniform ground cover runoff erosion is modeled based on a power function of excess shear stress in which shear stress efficiency is inversely proportional to vegetation cover this approach is validated using data plant effect on slope stability is represented by additional cohesion provided by plant roots vegetation cover is assumed to reduce sediment transport rates due to physical creep processes rainsplash dry ravel and expansion and contraction of sediments according to a negative exponential relationship vegetation grows as a function of both available cover and unoccupied space by plants and is killed by geomorphic disturbances runoff erosion and landsliding and wildfires analytical results suggest that in an equilibrium basin with a fixed vegetation cover plants may cause a transition in the dominant erosion process at the channel head a runoff erosion dominated landscape under none or poor vegetation cover may become landslide dominated under a denser vegetation cover the sign of the predicted relationship between drainage density and vegetation cover depends on the relative influence of vegetation on different erosion phenomena with model parameter values representative of the oregon coast range ocr numerical experiments conducted using the channel hillslope integrated landscape development child model confirm the findings based on the analytical theory a highly dissected fluvial landscape emerges when surface is assumed bare when vegetation cover is modeled landscape relief increases resulting in hollow erosion dominated by landsliding interestingly our simulations underscore the importance of vegetation disturbances by geomorphic events and wildfires on the landscape structure simulated landscapes resemble real world catchments in the ocr when such disturbances are considered

the radial diffusion method 1 using intact cores to determine isotopic composition chemistry and effective porosities for groundwater in aquitards a new method is described for the determination of the isotopic composition and chemistry of groundwater in aquitards the effective porosities for each component can be determined concurrently the method is based on diffusive exchange of water and solutes between groundwater in a cylindrical core of aquitard material and water in a reservoir placed along the axis of the cylinder the method was tested for 2h cl and so4in an aquitard consisting of clay rich glacial till the 2h in aquitard core samples as determined by radial diffusion agreed closely with 2h in groundwater obtained from corresponding piezometers installed in the aquitard for the concentrations of cl and so4 the agreement was less close but still satisfactory the effective porosities were equal to the total porosities for 2h and were less than the total porosities for cl and so4 ions

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

detection of transience in eroding landscapes past variations in climate and tectonics have led to spatially and temporally varying erosion rates across many landscapes in this contribution i examine methods for detecting and quantifying the nature and timing of transience in eroding landscapes at a single location cosmogenic nuclides can detect the instantaneous removal of material or acceleration of erosion rates over millennial timescales using paired nuclides detection is possible only if one of the nuclides has a significantly shorter half life than the other currently the only practical way of doing this is to use cosmogenic in situ carbon 14 14c alongside a longer lived nuclide such as beryllium 10 10be hillslope information can complement or be used in lieu of cosmogenic information in soil mantled landscapes increased erosion rates can be detected for millennia after the increase by comparing relief and ridgetop curvature this technique will work as long as the final erosion rate is greater than twice the initial rate on a landscape scale transience may be detected based upon disequilibria in channel profiles or ridgetops but transience can be sensitive to the nature of transient forcing where forcing is periodic landscapes display differing behavior if forcing is driven by changes in base level lowering rates versus changes in the efficiency of either channel or hillslope erosion e g driven by climate change oscillations in base level lowering lead to basin averaged erosion rates that reflect a long term average erosion rate despite strong spatial heterogeneity in local erosion rates this averaging is reflected in 10be concentrations in stream sediments changes in hillslope sediment transport coefficients can lead to large fluctuations in basin averaged erosion rates which again are reflected in 10be concentrations the variability of erosion rates in landscapes where both the sediment transport and channel erodibility coefficients vary is dominated by changes to the hillslope transport coefficient copyright 2016 john wiley sons ltd

transient quaternary erosion and tectonic inversion of the northern range trinidad abstract cosmogenic 10be measured in sediments from northern range catchments on the island of trinidad reveals low millennial scale rates of erosion average 40 mm ka that increase roughly eightfold from 11 to 92 mm ka eastward across the mountain range these results in conjunction with an analysis of mountain morphometrics are consistent with quaternary east side up tilting of the northern range which has occurred recently 100 ka the highest millennial scale erosion rates coincide spatially with quaternary east side surface uplift albeit not in magnitude high modern rainfall rates low topographic relief and convex longitudinal stream profiles indicating transient quaternary erosion we interpret that hillslope adjustment and erosion of the northern range is buffered from climatic and tectonic forcings by dense tropical vegetation cover thick saprolite and porous regolith compared with longer term thermochronology exhumation rates we document that an order of magnitude deceleration of and reversal in the locus of erosion and exhumation has occurred during the pliocene to the holocene we suggest that these combined data sets highlight distinct syn and post collisional phases of northern range development that are related to a major change in relative caribbean south american plate motion from oblique convergence to transform motion oblique collision during the mid miocene likely caused relatively higher rates of and asymmetric exhumation of the northern range post collisional mountain scale tilting is likely caused by a combination of crustal extension in the gulf of paria and by deep subsurface lithospheric detachment processes that drives dynamic topography

drainage density and relative relief in humid steep mountains with frequent slope failure previous studies in japanese mountains have shown that drainage density d correlates negatively with relief r and the erosion rate e whereas elsewhere both r and e correlate positively with d to investigate the inconsistency this paper compares two types of d r relations for eight mountain river basins in central japan r is computed from a digital elevation model for 1109 morphometric samples of area 0 5 km 0 5 km drainage networks in these cells were first constructed by map criteria applied previously in japan deeply notched v shaped contours with an angle 53 the resulting d correlates negatively with r confirming preceding studies when drainage lines along shallower hollows were added however the calculated d essentially constant these relations arise from active landsliding in high relief terrains which has eroded steep channel banks into gentle ones the decline of channel banks with increasing r is accelerated in terrains underlain by soft rocks because of rapid erosion the constant d for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains because the d r and d e relations for japan reflect a uniquely japanese physiographic setting characterized by frequent landsliding they differ from those relations for other regions where channelization by gullying predominates 1997 by john wiley sons ltd

characterizing the hydrogeology of a complex clay rich aquitard system using detailed vertical profiles of the stable isotopes of water abstract high resolution 1d profiles of the stable isotopes of porewater 2h and 18o obtained by direct porewater equilibration of core samples were used to identify hydrogeologic zones in a thick complex till aquitard system in saskatchewan canada detailed 1d isotope profiles revealed the presence of three distinct hydrogeological zones an upper 5 10 m an intermediate 10 30 m and a lower 30 62 5 m till zone the upper hydrogeological zone was controlled by a sand layer having a high hydraulic conductivity k the lack of vertical variability in the stable isotope data in the intermediate zone suggested groundwater flow and solute transport was controlled by a system of interconnected vertical fractures and lateral sand layers the curved shape of the isotope profile in the lower till zone suggested that solute transport in this zone was controlled mainly by molecular diffusion we show that high resolution vertical stable isotope profiles of porewater obtained from core samples and direct equilibration yield cost effective and invaluable hydrogeologic information on groundwater flow in aquitard systems that cannot be realistically obtained by construction of costly conventional piezometer bundles i e 2h and 18o analyses of water samples and k determinations further the direct equilibration approach overcomes the problem of piezometer leakage in low k aquitards

factors controlling shelf sediment dispersal along the southeast african continental margin abstract four major factors control sediment dispersal along the southeast african continental margin 1 morphology of the upper continental margin 2 wave regime and wind driven circulation 3 influence of the agulhas current and 4 sediment supply these factors interact on various scales to produce a unique regional sediment dispersal pattern the continental shelf is very narrow and the adjacent slope extremely steep the shelf platform is interrupted by a number of structural offsets and locally the shelf break is dissected by numerous submarine canyons the nearshore zone down to about 60 m waterdepth is dominated by a high energy swell regime and in most places is underlain by a thin wedge of sandy sediment this wedge appears to have achieved dynamic equilibrium with the prevailing energy regime and additional sediment is rapidly dispersed and fed into a sandstream situated on the central shelf where the agulhas current dominates sediment transport along some parts of the coast the sediment wedge is dammed behind a drowned coastal dune ridge within the sandstream sediment is transported alongshelf until a structural offset is reached where sediment spills over the shelf break four major localities for off shelf transport are recognized between maputo and port elizabeth most of the suspended load appears to be expelled from the system without being deposited on the shelf in the lee of each offset a clockwise gyre is developed which produces return flow currents capable of moving sediment northward thereby creating bedload partings in the vicinity of these partings depositional features are observed that are similar to those normally associated with tidal regimes e g bedforms migrating in opposite directions most of the bedload sediment entering the system is eventually deposited in well defined sinks situated in the lee of structural offsets this model applies only to inter glacial high sea level situations accompanied by strong western boundary flow of the agulhas current

chlorine transport processes through a 2000 m aquifer aquitard system abstract in the paris basin in france the callovo oxfordian cox is currently studied over a 250 km2 surface area by the french national radioactive waste management agency in order to assess the feasibility of long term underground nuclear waste repository the cox is a 140 m thick clay rich layer which is part of the 2000 m aquitard aquifer system constituting the sedimentary cover in such sedimentary context the transport processes of potential contaminants can be represented by both vertical diffusion and horizontal advection through the most permeable layers chloride is used as a natural conservative tracer and is monitored in term of concentrations and isotopic composition 37cl for both pore and groundwater during this study the samples were collected from three boreholes located in the center of the studied zone one of them est433 going down to 2000 m depth the main solute transport process is shown to be vertical diffusion from the massive keuper halite level to the rest of the sedimentary pile this global diffusive system can be occasionally disturbed by horizontal circulation of groundwater occurring in the oxfordian and dogger limestone formations therefore these circulations cut the global diffusive system in a succession of independent diffusive systems in this study the data set was implemented in a simplified 2d solute transport model and scenarii reproducing known history in term of paleo circulations inside the system were applied and allowed to obtained a good fit of the data model results showed that paleo circulations occurring between 145 ma and 110 ma still have an impact on current distribution of chloride in the system especially for 37cl the model highlights the need of the presence of a circulation spatially limited at the base of the liassic formation to fit the data the best fit obtained indicated current residence time of 500 ka in the dogger and oxfordian with respective onset of the circulations at 20 ma and 5 ma

latest pleistocene holocene debris flow activity santa catalina mountains arizona implications for modern debris flow hazards under a changing climate abstract hazard mitigation for extreme events such as debris flows requires geologic mapping and chronologic information particularly for alluvial fans near mountain fronts in the southwestern united states in july 2006 five consecutive days of monsoonal storms caused hundreds of debris flows in southeastern arizona particularly in the southern santa catalina mountains north of tucson before 2006 no historical debris flows from the santa catalina mountains reached the populated mountain front although abundant evidence of prehistoric debris flows is present on downslope alluvial fans we used a combination of surficial geologic mapping and 10 be exposure dating to produce a debris flow history for pima and finger rock canyons the largest debris flows of latest pleistocene to early holocene age covered much of the apices of alluvial fans formed at the mouths of these canyons and extended up to 3 km downslope these debris flow deposits were inset against higher and older alluvial surfaces with few debris flow deposits of late pleistocene age the 10 be ages in this study have considerable scatter for surfaces believed to be of uniform age indicating the dual possibilities of inheritance from previous cosmic ray exposure as well as the potential for composite deposits derived from numerous debris flows we then used an empirical inundation model laharz to assess probable magnitudes of the older debris flows to evaluate possible initiation mechanisms in channel and terrace storage within the canyons is not sufficient to generate volumes likely needed to produce the larger late pleistocene to early holocene debris flow deposits the abundance of latest pleistocene and early holocene deposits suggests that large debris flows were generated during the instability associated with climate and vegetation changes at the pleistocene holocene transition under present watershed conditions with limited sediment supplies modern debris flow hazards are generally limited to within mountains and near mountain fronts

the landscape evolution observatory a large scale controllable infrastructure to study coupled earth surface processes abstract zero order drainage basins and their constituent hillslopes are the fundamental geomorphic unit comprising much of earth s uplands the convergent topography of these landscapes generates spatially variable substrate and moisture content facilitating biological diversity and influencing how the landscape filters precipitation and sequesters atmospheric carbon dioxide in light of these significant ecosystem services refining our understanding of how these functions are affected by landscape evolution weather variability and long term climate change is imperative in this paper we introduce the landscape evolution observatory leo a large scale controllable infrastructure consisting of three replicated artificial landscapes each 330 m 2 surface area within the climate controlled biosphere 2 facility in arizona usa at leo experimental manipulation of rainfall air temperature relative humidity and wind speed are possible at unprecedented scale the landscape evolution observatory was designed as a community resource to advance understanding of how topography physical and chemical properties of soil and biological communities coevolve and how this coevolution affects water carbon and energy cycles at multiple spatial scales with well defined boundary conditions and an extensive network of sensors and samplers leo enables an iterative scientific approach that includes numerical model development and virtual experimentation physical experimentation data analysis and model refinement we plan to engage the broader scientific community through public dissemination of data from leo collaborative experimental design and community based model development

ecohydrologic role of solar radiation on landscape evolution solar radiation has a clear signature on the spatial organization of ecohydrologic fluxes vegetation patterns and dynamics and landscape morphology in semiarid ecosystems existing landscape evolution models lems do not explicitly consider spatially explicit solar radiation as model forcing here we improve an existing lem to represent coupled processes of energy water and sediment balance for semiarid fluvial catchments to ground model predictions a study site is selected in central new mexico where hillslope aspect has a marked influence on vegetation patterns and landscape morphology model predictions are corroborated using limited field observations in central nm and other locations with similar conditions we design a set of comparative lem simulations to investigate the role of spatially explicit solar radiation on landscape ecohydro geomorphic development under different uplift scenarios aspect control and network control are identified as the two main drivers of soil moisture and vegetation organization on the landscape landscape scale and long term implications of these short term ecohdrologic patterns emerged in modeled landscapes as north facing slopes nfs get steeper by continuing uplift they support erosion resistant denser vegetation cover which leads to further slope steepening until erosion and uplift attains a dynamic equilibrium conversely on south facing slopes sfs as slopes grow with uplift increased solar radiation exposure with slope supports sparser biomass and shallower slopes at the landscape scale these differential erosion processes lead to asymmetric development of catchment forms consistent with regional observations understanding of ecohydrogeomorphic evolution will improve to assess the impacts of past and future climates on landscape response and morphology

coupled study of water stable isotopes and anions in porewater for characterizing aqueous transport through the mesozoic sedimentary series in the eastern paris basin abstract this study presents data on chloride and bromide concentrations in porewater water and anion diffusion coefficients and their accessible porosities based on radial diffusion experiments on rock samples collected from a 2000 m deep borehole est433 drilled by andra in the eastern paris basin the distributions of water stable isotope and chloride concentrations in porewater along this column reveal transient flows of water and solutes between the aquitard layers and the surrounding aquifers these distributions confirm the occurrence of two separate aquitard aquifer systems oxfordian callovo oxfordian dogger and dogger liassic rhaetian this separation is confirmed by cl br ratios which are low in liassic and dogger porewater suggesting the influence of primary brines and which are close to the marine ratio in the dogger groundwater based on these results transport simulations in the two systems were carried out according to different scenarios the simulation results confirm that transport properties obtained in the laboratory at sample scale may be extrapolated to the formation scale it is highly probable that diffusion is the main transport process in the callovo oxfordian formation this may also be the case in the dogger liassic layer although a limited contribution from advection cannot be totally excluded by testing different scenarios of boundary conditions in diffusive models it is proposed that the dogger aquifer was first activated in the early miocene

geochemistry and origin of formation brines from the paris basin france 2 saline solutions associated with oil fields abstract oil fields from the paris basin are located in three geological levels dogger middle jurassic rhaetian and keuper upper triassic the origin of water and dissolved salts in saline solutions associated with oil is investigated using the hypothesis that cl and br are conservative in solution in a diagram of cl br ratios vs cl the points of the dogger and the keuper aquifers lie in the zone of primary brines whereas those of the rhaetian are located in the zone of secondary brines the na cl ratio is very high in all of the saline solutions suggesting either a relatively poorly evolved brine at the beginning of halite deposition or some halite dissolution all of the saline solutions especially those from the dogger aquifer are clearly diluted dilution by meteoric waters would not alter the cl br ratio high concentrations of lithium rubidium and boron are attributed to the presence of an extremely evolved brine of marine origin in mixtures of secondary brines formed by dissolution of halite and small amounts of sylvite and ca sulphate mass balance calculations of the excess of cl with respect to na k allows the fraction x of water derived from the primary brine to be calculated assumptions are that all na and k is derived from the secondary brine and that the cl content of the primary brine is constrained by bischofite saturation at 11 000 mmol kg 1 the typical proportion of water from the primary brine waters is 0 7 in the dogger formation and 2 4 in the keuper values of the concentration factor cf expressed as the ratio of the molal concentration of a conservative ion in the evolved brine to its concentration in seawater have been calculated for lithium solutions from the dogger and keuper aquifers have cfli values of 1 8 103 and of 7 7 103 respectively in the rhaetian aquifer the linear relationship between heavy isotope contents of the brine 2h and 18o and the cl content indicates a mixture of two water sources the first one is meteoric water as defined by the intersection of the formation water line with the global meteoric water line 2 h 65 18 o 9 3 the other end member is enriched in heavy isotopes and in cl and is attributed to seawater that has dissolved evaporites mainly halite however the presence of small amounts of an extremely evolved brine is required to account for the bromide lithium rubidium and boron contents of the formation brine from the rhaetian aquifer as this contribution is very limited in amount it cannot affect the heavy isotope content of the formation water mass balance equations are solved for ternary mixtures of meteoric water seawater and brine the same constraints as above no na and k supplied by the primary brine and clbrine 11 000 mmol kg 1 are applied it is also assumed that the seawater component has the same ionic contents as modern seawater and that the salt content of the meteoric component is negligible the fraction of primary brines is x 1 4 according to the cl balance this estimate agrees with that obtained from the lithium balance assuming that the primary brine component was the same as that of the keuper formation water mass balance calculations also indicate that the so42 content of the rhaetian formation water is exclusively due to the secondary brine component in the three saline solutions the very high ca2 contents and high ca 2 mg 2 ratios may be attributed to reaction of the very evolved brine free of so2 4 with gypsum or anhydrite the result is an exchange of mg2 for ca2 which causes a release of ca2 to the solution and a precipitation of secondary mg sulphate this process can also account for the high strontium contents of the analysed samples values of the ratio 87 sr 86 sr are very high in the keuper formation water due to close contact of the solutions with the granitic basement or with granite derived detrital deposits values in the rhaetian and dogger aquifers equal those of upper triassic marine deposits the stable isotope 34s and 18o content of the dissolved aqueous so2 4 indicates a triassic origin for the bulk of sulphate involved in the evolution of formation waters from the rhaetian and from the dogger all geochemical indicators thus show a vertical migration of triassic brines however aqueous so2 4 from the keuper has a permian isotopic signature suggesting a reworking in solution of salts from this period

widespread cementation induced by inflow of continental water in the eastern part of the paris basin o and c isotopic study of carbonate cements abstract mesozoic limestones from the eastern part of the paris basin display mostly in strata rich in bioherms abundant macro cavities vugs and some connected micro fractures almost completely filled with euhedral calcite crystals late calcite spar the interparticle porosity of limestones is also filled with euhedral calcite spar cements similar to those observed in vugs and fractures and rarely displays the preservation of the structures typical of early marine cements these calcite spars both from vugs fractures infillings and from cemented porosity were studied in drilled cores cross cutting the kimmeridgian to bathonian series with the main objective of determining the nature and flow regime of the fluids responsible for the strong porosity reduction observed in that part of the paris basin mesozoic limestones the approach combined mineralogical and geochemical studies o and c stable isotopic compositions measured by conventional and sims methods with temperature estimates from fluid inclusion analyses the 13 c values of late calcite are close to those of the host limestones and correlate with the 13 c changes in host rocks indicating a local source of c by contrast late calcites from vugs fractures and also in the cemented interparticle porosity of limestones have 18 o values around 21 smow values which are distinct from those of bulk host limestones 25 to 27 the 18 o value of the fluid is estimated to be 6 8 to 2 5 for a crystallisation temperature between 32 and 42 c determined from fluid inclusion studies thus the parent fluid of cemented interparticle porosity and vug and fracture infillings likely contained a component of meteoric water in contrast to the previous belief that the reduction of porosity in those series was related to early marine diagenesis possible situations in which such meteoric fluid could have occurred are i a stage when the limestone aquifers were directly connected to surface water and or ii channelling of water from deeper zones in the basin through regional fault systems the o isotopic compositions of the calcite cements in the underlying 140 m thick callovo oxfordian argillites and those of the less recrystallised bathonian to kimmeridgian limestones are those expected for unmodified marine calcite 18 o ca 28 smow therefore from the isotopic point of view the callovo oxfordian argillites remained essentially unaffected by the paleo fluid circulation documented in the adjacent limestones series this indicates the argillites acted as an efficient permeability barrier in the past

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

chlorine transfer out of a very low permeability clay sequence paris basin france 35cl and 37cl evidence abstract the marine callovo oxfordian clay formation is found at a depth around 410m in the eastern part of the paris basin france it is a very low permeability formation investigated by the french agency for nuclear waste management andra to study the feasibility of a radioactive waste disposal examining hydrogeological and geochemical characteristics of the clay sequence may test confinement properties of this formation this study uses chlorine isotopes to investigate long term transport processes which may carry chemical elements out of the clay layer to the surrounding rocks detailed chlorine concentration and 37cl depth profiles are examined using pore waters and aquifer waters sampled in the clay formation and its surrounding aquifers the dogger at the bottom and the oxfordian kimmeridgian tithonian unit at the top they are discussed in terms of chlorine budget and hydrogeological processes clay pore waters and aquifer waters show strong chlorine concentration depletion a steep cl concentration gradient from the dogger at 500m in depth 2500 mg l to the oxfordian kimmeridgian tithonian aquifer near the surface 10 mg l is associated to a v shaped profile of the 37cl values modelling cl transport shows that a hydrodynamic dispersion process explains cl concentration and 37cl profiles in oxfordian limestone this process implies a mean upward flux of chloride in the 2 6 10 8 8 2 10 8 mole m2 yr range from the clay formation towards upper limestones where a westward advective flow disperses the chloride the modelling and knowledge of underground water transfer suggest a maximum effective cl hydrodynamic vertical dispersion coefficient vertical cl transport coefficient of 7 6 10 10 m2 s chlorine transfer through the callovo oxfordian clay since deposition 160my ago can be mainly described by the interplay of an early dilution and a later hydrodynamic dispersion event which has apparently erased most of the isotopic effects of diagenetic events such as early diffusion ion filtration etc

diffusion as the main process for mass transport in very low water content argillites 2 fluid flow and mass transport modeling 1 on the basis of chloride concentrations of pore water in the tournemire massif part 1 a conceptual model for mass transport in argillites by diffusion is proposed from this conceptual model and current knowledge of the geological history of the massif one dimensional numerical simulations are formulated for chloride transport in tournemire massif over the past 53 ma good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is the main process for mass transport in the massif this model is also tested using deuterium contents of pore water applying variable concentrations to meteoric water circulating in system boundary layers based on the thermal dependency of its isotopic composition these simulations reveal the likely important role of lithologic heterogeneities such as fractures in the horizontal distribution of tracer concentrations

controls on the spacing of first order valleys 1 many landscapes are composed of ridges and valleys that are uniformly spaced even where valley locations are not controlled by bedrock structure models of long term landscape evolution have reproduced this phenomenon yet the process by which uniformly spaced valleys develop is not well understood and there is no quantitative framework for predicting valley spacing here we use a numerical landscape evolution model to investigate the development of uniform valley spacing we find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area a proxy for water flux and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium valley spacing is most sensitive to the relative rates of advective erosion processes such as stream incision and diffusion like mass transport such as soil creep and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a peclet number we use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape the observed scaling relationships also provide insight into the cause of transitions from rill like drainage networks to branching networks the spatial scale of first order drainage basins the contributing area at which hillslopes transition into valleys and the narrow range of width to length ratios of first order basins

the effects of climate and landscape position on chemical denudation and mineral transformation in the santa catalina mountain critical zone observatory abstract understanding the interactions of climate physical erosion chemical weathering and pedogenic processes is essential when considering the evolution of critical zone systems interactions among these components are particularly important to predicting how semiarid landscapes will respond to forecasted changes in precipitation and temperature under future climate change the primary goal of this study was to understand how climate and landscape structure interact to control chemical denudation and mineral transformation across a range of semiarid ecosystems in southern arizona the research was conducted along the steep environmental gradient encompassed by the santa catalina mountains critical zone observatory scm czo the gradient is dominated by granitic parent materials and spans significant range in both mean annual temperature 10 c and precipitation 50 cm a 1 with concomitant shift in vegetation communities from desert scrub to mixed conifer forest regolith profiles were sampled from divergent and convergent landscape positions in five different ecosystems to quantify how climate landscape position interactions control regolith development regolith development was quantified as depth to paralithic contact and degree of chemical weathering and mineral transformation using a combination of quantitative and semi quantitative x ray diffraction xrd analyses of bulk soils and specific particle size classes depth to paralithic contact was found to increase systematically with elevation for divergent positions at approximately 28 cm per 1000 m elevation but varied inconsistently for convergent positions the relative differences in depth between convergent and divergent landscape positions was greatest at the low and high elevation sites and is hypothesized to be a product of changes in physical erosion rates across the gradient quartz plagioclase q p ratios were used as a general proxy for bulk regolith chemical denudation q p was generally higher in divergent landscape positions compared to the adjacent convergent hollows convergent landscape positions appear to be collecting solute rich soil waters from divergent positions thereby inhibiting chemical denudation clay mineral assemblage of the low elevation sites was dominated by smectite and partially dehydrated halloysite whereas vermiculite and kaolinite were predominant in the high elevation sites the increased depth to paralithic contact chemical denudation and mineral transformation are likely functions of greater water availability and increased primary productivity landscape position within a given ecosystem exerts strong control on chemical denudation as a result of the redistribution of water and solutes across the landscape surface the combined data from this research demonstrates a strong interactive control of climate landscape position and erosion on the development of soil and regolith

introduction to present and past transfers in a sedimentary aquifer aquitard system a 2000 m deep drill hole in the mesozoic of the paris basin

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

increased sediment transport via bioturbation at the last glacial interglacial transition global sedimentation rates increased during the quaternary due to frequent landscape adjustment to climatic oscillations although high rates of sediment transport are commonly associated with glacial conditions in mountainous terrain the infl uence of climate and vegetation on geomorphic response is poorly constrained outside of glaciated settings along a low gradient 30 hillslope valley transect on a moderately dissected loess mantled fl uvial terrace in the charwell basin new zealand we coupled records of colluvial infi lling and vegetation change via phytoliths to show that late pleistocene sediment fl ux was 0 0012 m 3 m 1 a 1 under a shrubland grassland mosaic and holocene sediment fl ux was 0 0022 m 3 m 1 a 1 under forest this near doubling through the last glacial interglacial transition appears to refl ect increased bioturbation and downslope soil transport associated with a forest ecosystem such an increase in sediment transport contrasts with a contemporaneous decrease inferred for adjacent steep landslide prone catchments suggesting that geomorphic response to climate change is heavily modulated by biology topography and geological substrate our fi ndings appear to contradict the commonly cited notion that forest colonization universally stabilizes soils and suppresses erosion instead over long time scales bioturbation associated with forests may increase transport along gentle portions of the landscape not subject to slope instability or erosion by overland fl ow

large scale tracer profiles in a deep claystone formation opalinus clay at mont russelin switzerland implications for solute transport processes and transport properties of the rock abstract natural tracers cl and stable water isotopes in pore water of the opalinus clay and adjacent formations were studied in the motorway tunnel at mont russelin switzerland the opalinus clay occurs in the core of an anticline which is cut by a complex system of thrust faults concentration profiles of natural tracers were taken from 17 boreholes along a 363 m long section pore waters of drillcore samples were analysed with indirect and direct methods the cl and stable water isotope distribution in the pore water shows a regular and well defined profile with a conspicuous decrease towards the overlying dogger limestone aquifer the highest cl values approximately 23 000 mg l are found in the core of the anticline in liassic claystones underlying the opalinus clay to quantify the large scale transport properties of the opalinus clay formation a 2d transport model was constructed and used to reproduce the observed concentration profiles the calculations indicate that the observed tracer distributions are consistent with diffusion as the dominant transport process groundwater flow in the overlying dogger aquifer was initiated about 2 4 ma ago which is long after the folding of the jura mountains and probably coincides with the exposure of the aquifer to freshwater recharge following continued erosion of the anticline the calculations suggest that tracer distributions are controlled by 1 the timing of freshwater recharge in the overlying limestone aquifer 2 the shape of the anticline and 3 the magnitude and the anisotropy ratio of diffusion coefficients

stochastic processes of soil production and transport erosion rates topographic variation and cosmogenic nuclides in the oregon coast range landscapes in areas of active uplift and erosion can only remain soil mantled if the local production of soil equals or exceeds the local erosion rate the soil production rate varies with soil depth hence local variation in soil depth may provide clues about spatial variation in erosion rates if uplift and the consequent erosion rates are sufficiently uniform in space and time then there will be tendency toward equilibrium landforms shaped by the erosional processes soil mantle thickness would adjust such that soil production matched the erosion previous work in the oregon coast range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported we quantify how soil production varies with soil thickness in the southern oregon coast range and explore further the issue of landscape equilibrium apparent soil production is determined to be an inverse exponential function of soil depth with a maximum inferred production rate of 268 m ma 1 occurring under zero soil depth this rate depends however on the degree of weathering of the underlying bedrock the stochastic and large scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth the spatial variation of soil depth neither supports nor rejects equilibrium morphology our observed catchment averaged erosion rate of 117 m ma 1 is however similar to that estimated for the region by others and to soil production rates under thin and intermediate soils typical for the steep ridges we suggest that portions of the oregon coast range may be eroding at roughly the same rate but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle copyright 2001 john wiley sons ltd

a mathematical model for steady state regolith production at constant erosion rate it has been hypothesized that many soil profiles reach a steady state thickness in this work such profiles were simulated using a one dimensional model of reaction with advective and diffusive solute transport a model rock is considered consisting of albite that weathers to kaolinite in the presence of chemically inert quartz the model yields three different steady state regimes of weathering at the lowest erosion rates a local equilibrium regime is established where albite is completely depleted in the weathering zone this regime is equivalent to the transport limited regime described in the literature with an increase in erosion rate transition and kinetic regimes are established in the transition regime both albite and kaolinite are present in the weathering zone but albite does not persist to the soil air interface in the weathering limited regime here called the kinetic regime albite persists to the soil air interface the steady state thickness of regolith decreases with increasing erosion rate in the local equilibrium and transition regimes but in the kinetic regime this thickness is independent of erosion rate analytical expressions derived from the model are used to show that regolith production rates decrease exponentially with regolith thickness the steady state regolith thickness increases with the darcy velocity of the pore fluid and in the local equilibrium regime may vary markedly with small variations in this velocity and erosion rate in the weathering limited regime the temperature dependences for chemical weathering rates are related to the activation energy for the rate constant for mineral reaction and to the h of dissolution while for local equilibrium regimes they are related to the h only the model illustrates how geochemical and geomorphological observations are related for a simple compositional system the insights provided will be useful in interpreting natural regolith profiles copyright 2010 john wiley sons ltd

natural tracer profiles across argillaceous formations argillaceous formations generally act as aquitards because of their low hydraulic conductivities this property together with the large retention capacity of clays for cationic contaminants has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste in several countries programmes are under way to characterise the detailed transport properties of such formations at depth in this context the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large scale and long term transport behaviour of these formations here tracer profile data obtained by various methods of pore water extraction for nine sites in central europe are compiled data at each site comprise some or all of the conservative tracers anions cl br water isotopes delta 18 o delta 2 h and noble gases mainly he based on a careful evaluation of the palaeo hydrogeological evolution at each site model scenarios are derived for initial and boundary pore water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites using transport parameters derived from laboratory or in situ tests the comprehensive results from this project have been reported in mazurek et al 2009 here the results for three sites are presented in detail but the conclusions are based on model interpretations of the entire data set in essentially all cases the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles transport by advection has a negligible influence on the observed profiles at most sites as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data the advantages and disadvantages of different conservative tracers are also assessed the anion cl is well suited as a natural tracer in aquitards because its concentration varies considerably in environmental waters it can easily be measured although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue the stable water isotopes are also well suited but they are more difficult to measure and their values generally exhibit a smaller relative range of variation chlorine isotopes delta 37 cl and he are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence it is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion leading to relatively sharp changes of boundary conditions can be considered as a pre requisite to obtain well interpretable tracer signatures on the other hand gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation

regolith thickness instability and the formation of tors in arid environments 1 we present model results suggesting that a physical erosion bedrock weathering feedback is responsible for the development of isolated bedrock knobs tors inselbergs that often punctuate otherwise smooth pediments of homogeneous basement lithology tors and larger more heavily jointed and morphologically complex exposures inselbergs may arise as a consequence of fluctuations in rainfall and sediment transport conditions combined with a bedrock weathering mechanism that depends on regolith thickness hydrogeochemical considerations and field observations in arid granitic environments suggest that the relationship between weathering rate and regolith thickness exhibits a maximum for a finite thickness of cover we have encapsulated this simple erosion weathering feedback in a numerical model simulating arid semiarid landscape evolution that produces low sloping pediments punctuated by tors tors form during periods of higher effective moisture resulting in local base level incision and regolith thinning on pediments invoking a transition in which mantled surfaces lower at rates exceeding the bare bedrock weathering rate this condition favors the emergence and growth of tors in areas covered by regolith thickness less than a threshold value subsequent shifts in climate or local base level that restore sediment surface lowering rates less than the bare bedrock weathering rate will lead to a progressive decrease in tor height and ultimately their disappearance thus according to this model tors in arid environments represent possibly transient features related to fluctuations in climate or local transport conditions rather than palimpsests of an ancient landscape derived from differential subsurface weathering followed by regolith stripping

weathering limited hillslope evolution in carbonate landscapes understanding topographic evolution requires integrating elementary processes acting at the hillslope scale into the long wavelength framework of landscape dynamics recent progress has been made in the quantification of denudation of eroding landscapes and its links with topography despite these advances data is still sparse in car bonate terrain which covers a significant part of the earth s surface in this study we measured both long term denudation rates using in situ produced 36 cl concentrations in bedrock and regolith clasts and surface convexity at 12 sites along ridges of the luberon carbonate range in provence southeastern france starting from 30 mm ka for the lowering of the summit plateau surface denudation linearly increases with increasing hilltop convexity up to 70 mm ka as predicted by diffusive mass transport theory beyond this point denuda tion rates appear to be insensitive to the increase in hilltop convexity we interpret this constant denudation as indicating a transition from a regime where hillslope evolution is primarily controlled by diffusive downslope regolith transport toward a situation in which denuda tion is limited by the rate at which physical and chemical weathering processes can produce clasts and lower the hilltop such an abrupt transition into a weathering limited dynamics may prevent hillslope 1 denudation from balancing the rate of base level fall imposed by the river network and could potentially explain the development of high local relief in many mediterranean carbonate landscapes

constraining porewater chemistry in a 250m thick argillaceous rock sequence the geochemistry of an argillaceous rock sequence from a deep borehole in ne switzerland was investigated the focus was to constrain the porewater chemistry in low permeability jurassic rocks comprising the liassic the opalinus clay formation the brown dogger unit and the effingen member malm a multi method approach including mineralogical analysis aqueous and ni ethylenediamine extraction squeezing tests and pco2 measurements as well as geochemical modelling was applied for this purpose a consistent dataset was obtained with regard to the main solutes in the porewaters a fairly constant anionaccessible porosity of 50 of the total porosity was deduced for all analysed samples which displayed variable clay mineral contents sulphate concentrations were shown to be constrained by a sulphate bearing phase presumably by celestite or a sr ba sulphate application of a simple equilibrium model including cation exchange reactions calcite and celestite equilibrium showed good agreement with squeezing data indicating the suitability of the modelling approach to simulate porewater chemistry in the studied argillaceous rocks the modelling highlighted the importance of correct determination of the exchangeable cation population the analysis corroborates that squeezing of the studied rocks is a viable and efficient way to sample porewater

minimizing the grid resolution dependence of flow routing algorithms for geomorphic applications the results of flow routing methods currently used in the geomorphic literature depend on grid resolution this poses a problem for landscape evolution models which must be independent of grid resolution to the greatest extent possible here i illustrate a refinement of currently used flow routing algorithms that yields unit contributing areas i e contributing areas per unit width of flow with minimal grid resolution effects i illustrate the application of this method in idealized topography in high resolution digital elevation models dems of real world topography and by integration into a landscape evolution model for ridge and valley topography the landscape evolution model produces grid resolution independent results in a more straightforward way than previous models for this type of landscape

predicting the thickness and aeolian fraction of soils in upland watersheds of the mojave desert abstract soil thickness and soil texture and their spatial variability at hillslope scales are important inputs for hydrologic models recent studies have demonstrated that mechanistic models can accurately predict the spatial distribution of soil thickness in areas where soil thickness varies gradually along hillslope profiles to date however these models have not been tested in arid regions where soils are often thin and highly variable at small scales i e 1 10 m and where the influence of aeolian accretion on soil thickness and soil texture may be significant in addition most of the data available for the fraction of the soil derived from aeolian deposition which can serve as a proxy for soil texture originate from soils developed on stable depositional landforms data for aeolian fractions from upland soils are scarce in this study we developed and tested a numerical model for the prediction of thickness and aeolian fraction of soils in arid upland areas the model assumes a long term balance between the rates of soil production from bedrock aeolian accretion and soil erosion rates of soil production are quantified in the model using the exponential and humped soil production functions and soil erosion rates are quantified using the nonlinear depth and slope dependent transport functions assuming that only the upper soil horizons a b are capable of transport the rate of aeolian deposition is assumed to be spatially uniform we calibrated the three free parameters of the model at a site in the mojave desert with a granite lithology using a combination of 1 field measured data for soil thickness and 2 estimation of the aeolian fraction in the soil using laboratory analysis of immobile element concentrations we validated the model results in three nearby sites using a combination of measured soil thickness in soil pits and the presence absence of soil and laboratory analysis of the aeolian fraction of soil the study area is characterized by generally thin soils

headwater channel dynamics in semiarid rangelands colorado high plains usa incised ephemeral channels provide a window into the fluvial processes that help sculpt rangeland landscapes this paper presents observations of ephemeral channels and valley networks in the high plains of colorado usa with an eye toward painting a picture of the ingredients that must be included in mathematical models of landscape evolution in such environments channel incision in the study area is driven by summer thunderstorms which can with reasonable frequency 3 5 yr generate boundary shear stresses high enough to penetrate the highly resistant vegetation armor but only within erosional hot spots where hydraulic forces are amplified by channel constriction and locally steep gradients focusing of erosion at these hot spots which correspond to knickpoints and channel heads is amplified by the small areal footprint and short erosional reach of most convective storms upstream migration of knickpoints creates a pattern of short active channel reaches separated by unchanneled or weakly channeled fully vegetated stable reaches based on our observations we interpret the necessary and sufficient conditions leading to the observed channel forms and dynamics as 1 a resistant vegetation layer overlying an erodible substrate which sets up a conditional instability through which erosional perturbations can grow by positive feedback 2 high flow variability 3 moderate to high substrate cohesion and 4 a high volume fraction of fine grained erodible material concave upward valley long profiles are interpreted as a trade off between downstream increasing flood frequency and downstream decreasing flood effectiveness the observed process dynamics imply that long term rates of valley incision should be especially sensitive to climatic oscillations between episodes of drought and warm season convective rainfall

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