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

distribution of beryllium between solution and minerals biotite and albite under atmospheric conditions and variable ph abstract biotite and albite grains having a size range from 20 to 124 m were suspended in be bearing solutions at ph 2 to 9 for periods of 30 min to 20 days the amount of be sorbed onto biotite is up to 40 times higher than onto albite under the same conditions and ph 7 at ph 6 the distribution of be between solution and solids is related to sorption but at ph 6 the solute concentration is strongly controlled by solubility of be oh 2 solid because of this solubility control the calculation of a distribution coefficient k d s c where s is be sorbed at equilibrium per mass or specific surface area of sorbent and c is the be concentration in solution at equilibrium seems to be valid only at ph 6 the k d increases with decreasing suspended particle concentration from 0 2 to 2 0 g l 1 for both minerals for biotite the k d also increases with the fine 20 63 m relative to the coarse 63 124 m size fraction even upon normalization to specific surface area the relatively small amount of be sorbed onto albite at ph 2 and 4 limited extensive evaluation and comparison the rate of be sorption onto biotite follows a logarithmic function and ranges from 0 8 to 1 0 10 11 mol cm 2 s 1 in ph 2 and 6 solutions respectively the time variation of sorbed be onto albite was insignificant with increasing ph the sorption of be onto biotite partly relates to the kinetics of cation release the results of experiments are discussed with respect to some examples of the distribution of be isotopes in continental aquatic systems

10be and 26al evidence for exceptionally low rates of australian bedrock erosion and the likely existence of pre pleistocene landscapes analysis of in situ produced 10be and 26al demonstrate that some australian inselbergs granitic domes are among the most stable geomorphic surfaces in the world eroding at rates as low as 0 6 m myr twenty isotopic analyses of ten samples suggest that the bare bedrock tops of these isolated granitic domes have been exposed to cosmic radiation for at least 0 5 myr and are eroding at a mean model rate less than 0 7 0 1 m myr n 6 isotopic analyses of samples collected from the top of mt wudinna little wudinna and yarwondutta rock are most consistent with continuous exposure during erosion on the other hand samples collected from the flanks of some domes and the tops of other domes have isotopic abundances suggestive of complex exposure histories including burial and reexposure these unique isotopic data provide the first quantitative information for evaluating longstanding but previously untested hypotheses regarding the antiquity and development of these enigmatic landforms and indicate that some eyre peninsula inselbergs are probably relict features of pre pleistocene landscapes

distribution and genesis of soils of the northeastern united states abstract the soils of the northeastern united states central and northern appalachians north of the glacial border are spodosols inceptisols alfisols and some entisols and histosols these soils are relatively young 12 18 ka climate frigid soil temperatures parent material acidic sandy and vegetation conifers are the major soil forming factors affecting the genesis of the spodosols while parent material calcareous material is a determining factor affecting the genesis of the alfisols the inceptisols of southern new england are slightly different better developed cambic horizon than those of the appalachian plateau the genesis of the alfisols of the unglaciated appalachian plateau and triassic lowlands are also significantly influenced by carbonates and basic minerals in their parent material ultisols are found only south of the glacial border ultisols on the appalachian plateau and in the northern ridge and valley are young soils and should be identified as parent material ultisols while those of the southern ridge and valley piedmont and coastal plain show significant soil development and should be identified as genetic ultisols the soils south of the glacial border on steep slopes have been affected significantly by erosion during the cold cycles of the pleistocene while soils on gentle slopes have been affected to a lesser degree much of the material eroded during the late pleistocene has accumulated on lower sideslopes as colluvium the erosional and depositional processes have resulted in a complex mosaic of moderate to well developed soils on the more stable landscape surfaces and moderate to weakly developed soils on the erosional and depositional surfaces

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

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

conductive versus convective thermal modelling of the bushveld complex time to decide a reply to the comment by cawthorn on robb and mungall 2020 earth planet sci lett 534 116084

short and long term delivery rates of meteoric 10be to terrestrial soils well constrained long term average meteoric 10be deposition rates are important when meteoric 10be is used as a chronometer or tracer of earth surface processes to constrain meteoric 10be delivery to terrestrial soils we estimate time integrated 10be deposition rates from meteoric 10be inventories measured in dated soils and compare these results to a new synthesis of short term measurements of 10be in precipitation comparison of these long term rates to short term measurements suggests that short term measurements likely predict long term meteoric 10be deposition rates within uncertainties of 20 in precipitation measurements it is possible to deconvolve the contribution of atmospherically produced primary meteoric 10be from recycled meteoric 10be delivered by terrestrial dust if a second isotope is measured that quantifies either the recycled or primary components of meteoric 10be deposition we use dust concentration dependent differences between 7be and 10be measurements to make new estimates of the recycled contribution to total meteoric 10be flux delivered to the earth s surface these dust corrected data show a strong linear dependence between precipitation amount and primary meteoric 10be flux concentrations of primary meteoric 10be in mid and low latitude precipitation vary predictably by latitude between 0 63 104 and 2 05 104 atoms cm3 of precipitation providing a first order estimate of primary meteoric 10be deposition for a given latitude and precipitation rate

sediment transport by dry ravel 1 dry ravel is a general term that describes the rolling bouncing and sliding of individual particles down a slope and is a dominant hillslope sediment transport process in steep arid and semiarid landscapes during fires particles can be mobilized by the collapse of sediment wedges that have accumulated behind vegetation on a daily basis particles may be mobilized by bioturbation and by small landslides experiments on a dry ravel flume indicate that a basic expression of the momentum equation predicts the distance traveled by particles propelled down a rough surface this equation is further elaborated to produce a nonlinear slope dependent transport equation for dry ravel that represents the rate at which sediment crosses a contour width of slope sediment traps installed on two hillslope transects near santa barbara california measured the flux from dry ravel initiated by bioturbation and the data support the form of the equation additionally a physical model based on the infinite slope stability analysis is proposed for the initiation of dry ravel by landsliding the analytical result from this model is supported by experiments and field data reported by others

the upper critical zone of the eastern bushveld complex precursor of the merensky reef the upper critical zone in the central sector of the eastern bushveld complex consists predominantly of norites although bronzitites anorthosites chromitites and other chromitic rocks appear at intervals in the sequence gabbronorites appear near the middle of the zone the rock sequence is divided into 14 principal units plus the series from the base of the merensky reef to the top of the bastard reef mineralogical compositions of successive units have been determined from modal analyses and compositions of bronzite and plagioclase in the various rock units have been determined by microprobe analysis the results indicate that although parts of the zone show normal fractionation the zone as a whole is not the product of progressive fractionation of a magma crystal settling appears to have played a relatively minor role in evolution of the zone successive pulses of parent magma into the chamber may account for some of the mineralogical and chemical variations but features of certain thick norite units suggest stratification of the magma in the chamber the study suggests that the merensky reef registers a sudden event in the bushveld magma chamber an event that altered the chemistry of the system and triggered precipitation of sulfides and platinoid minerals the alternative hypothesis that the reef is the culmination of a long period of magma fractionation is not supported by the evidence presented chromite occurs in a variety of associations with plagioclase and bronzite the associations are consistent with phase relations in the system mg 2 sio 4 iron oxide caal 2 si 2 o 8 sio 2 at elevated pressure

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

glacial and periglacial erosion of the appalachians abstract the marine 18 o record indicates that the first ice advance into the appalachians equivalent to that of the late wisconsin occurred in the pliocene at about 2 4 ma only periodic localized glacial and periglacial activity occurred in the northern appalachians from 2 33 to 0 85 ma after 0 85 ma middle to late pleistocene eight out of ten glaciations covered the northern appalachians and brought periglacial conditions to the southern appalachians during the last 850 000 years glaciation extended to the late wisconsin limit within the appalachians for 15 of the time and extended to the early wisconsin limit just north of the appalachians for 25 of the time pleistocene glacial erosion of the appalachians of 120 200 m is necessary to account for the estimated volume of pleistocene ocean sediment derived from the appalachians and the estimated volume of pliocene pleistocene glaciogenic ocean sediment derived from the entire laurentide ice sheet this amount of glacial erosion occurring over the maximum expectable duration of pliocene pleistocene ice cover of 247 000 years yields glacial erosion rates from 0 5 0 8 m ka 1 such depths of erosion by thick warm based ice streams were localized in the lowlands and estuaries of the northern appalachians in the maritimes the presence of thin cold based ice caused minimal erosion of uplands periglacial landforms and tundra boreal forest were distributed throughout the appalachian highlands and the northern coastal plain during the glacial maxima periglacial erosion of 0 15 0 30 m ka 1 near the ice in pennsylvania decline to 0 1 0 2 m ka 1 in the southern piedmont each cold period almost completely renewed the regolith by eroding slopes and filling valleys the cumulative effect of the eight to ten major cold events could have produced as much as a few ten s of meters of periglacial ridge top lowering during the pleistocene both estimated glacial and periglacial erosion rates greatly exceed estimated current fluvial erosion rates therefore glacial and periglacial processes should be considered the dominant processes in shaping the present appalachian landscape the northern appalachians may be evolving towards a form where the landscape provides just the shape necessary to permit the least work conveyance of the ice across the region during glacial maxima the southern appalachians may be evolving towards a form where the landscape provides just the hillslope form necessary to transport the debris provided by periglacial conditions

calibrating a long term meteoric 10be accumulation rate in soil 1 using 13 samples collected from a 4 1 meter profile in a well dated and stable new zealand fluvial terrace we present the first long term accumulation rate for meteoric 10 be in soil 1 68 to 1 72 10 6 at cm 2 yr integrated over the past 18 ka site specific accumulation data such as these are prerequisite to the application of meteoric 10 be in surface process studies our data begin the process of calibrating long term meteoric 10 be delivery rates across latitude and precipitation gradients our integrated rate is lower than contemporary meteoric 10 be fluxes measured in new zealand rainfall suggesting that long term average precipitation dust flux or both at this site were less than modern values with accurately calibrated long term delivery rates such as this meteoric 10 be will be a powerful tool for studying rates of landscape change in environments where other cosmogenic nuclides such as in situ 10 be cannot be used

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

quantification of the effect of plants on weathering studies in iceland the weathering of calcium and magnesium silicate minerals on the continents has exerted a major control on atmospheric co 2 over geologic time and vascular plants may have played an important role in this process in western iceland we have examined the role of plants in weathering by measuring the chemistry of waters draining adjacent areas of basaltic rocks that are either barren having a partial cover of mosses and lichens or populated by trees the study area was chosen to maximize vegetational differences and to minimize differences in microclimate slope and lithology while avoiding hydrothermal waters and anthropogenic acid rain results including data on cation uptake by growing trees indicate that the rate of weathering release of ca and mg to streams and vegetation is two to five times higher in vegetated areas than the release of ca and mg to streams in barren areas this finding suggests a major role for vascular plants in accelerating weathering and thereby lowering atmospheric co 2 as they invaded upland areas of the continents between 380 and 350 ma

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

10be distribution in soils from merced river terraces california abstract the distribution and residence time of cosmogenic 10 be in clay rich soil horizons is fundamental to understanding and modelling the migration of 10 be on terrestrial sediments and in groundwater solutions we have analyzed seven profiles of clay rich soils developed from terrace sediments of the merced river california the terraces and soils of increasing age are used to compare the 10 be inventory with a simple model of accumulation decay and erosion the data show that the distribution of 10 be varies with soil horizon clay content that the residence time of 10 be in these horizons exceeds 10 5 years and that to a rough approximation the inventory of 10 be in a thoroughly sampled soil profile fits the equation n q em 1 e where q is delivery rate e is erosion rate m is the concentration of 10 be in the eroding surface layer is the decay constant and t is the age of the depositional unit from which the soil has developed the general applicability of this model is uncertain and warrants further testing in well calibrated terrace sequences

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

the global average production rate of10be precipitation collected in continuously open containers for about a year at seven sites around the united states was analyzed for10be 90sr 210pb and238u based on these data and long term precipitation 90sr and210pb delivery patterns the stratospheric tropospheric and recycled10be components in the collections were estimated and the global10be production rate was assessed single station production rate estimates range from 0 52 106 atoms cm 2 yr 1 to 2 64 106 atoms cm 2 yr 1 the mean value is 1 21 106 atoms cm 2 yr 1 with a standard error of 0 26 106 atoms cm 2 yr 1

tracing hillslope sediment production and transport with in situ and meteoric 10be 1 we use in situ produced and meteoric 10be analyzed in soils from 28 pits on four hillcrest parallel transects along a 14 hillslope in the great smoky mountains north carolina as tracers of soil production and transport we rely upon amalgamation both to investigate and smooth spatial variability in 10be concentrations lidar indicates that the hillslope is topographically complex and that soil is moved downslope diffusively until it encounters the ephemeral channel network and is rapidly exported in situ produced 10be measured in depth profiles indicates that over millennial timescales soils are mixed above the soil saprolite boundary in contrast meteoric 10be concentrations increase with depth and are correlated to concurrent increases of dithionite extractable al and ph observations explained by similar al and be mobility in the soil the concentrations of both meteoric and in situ produced 10be increase downslope proportional to the maximum soil particle path length the data suggest virtual downslope soil velocities of 1 1 1 7 cm yr 1 in a well mixed active transport layer 60 cm thick the thickness of this transport layer is constant downslope and depends on the rooting depth and consequent root wad thickness of downed trees on the slope both of which reflect depth to the soil saprolite boundary both meteoric and in situ produced 10be suggest that soil production is balanced by surface denudation at rates between 10 and 13 m myr 1 soil residence times on the slope range from 21 to 33 kyr based on the meteoric 10be inventories major element geochemical analysis suggests little if any elemental loss during soil transport downslope

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

using meteoric 10be to track fluvial sand through the waipaoa river basin new zealand we use meteoric 10 be measured in 24 fluvial sand samples collected along the mainstem and from prominent tributaries within the tectonically active waipaoa river basin new zealand to identify sediment sources and monitor the mixing of sediment as it travels from headwater basins to the sea deforestation for agriculture beginning in the early 1900s resulted in severe but nonuniformly distributed erosion tributaries in the northern headwaters where large amphitheater gullies that continually feed prodigious amounts of deeply sourced sediment to the mainstem are prevalent yield exceptionally low concentrations of meteoric 10 be 1 5 10 6 atoms g 1 in the more stable eastern and western tributaries concentrations of meteoric 10 be are nearly an order of magnitude greater 14 10 6 atoms g 1 meteoric 10 be concentrations in samples collected along the mainstem above and below tributary confluences steadily and regularly increase downstream r 2 0 92 as large amounts of low concentration gully derived sediments are augmented with higher concentration sediment from more stable tributaries providing strong evidence that meteoric 10 be concentrations reflect sediment sourcing in this fluvial network a two component mixing model indicates that the gullied northern region of the waipaoa basin produces sediment at a rate 20 times that of the eastern and western regions these results suggest that meteoric 10 be in contrast to the widely applied in situ technique that is limited by the availability and distribution of quartz is an effective tool for the rapid assessment of sediment dynamics and movement within a wide range of fluvial networks

meteoric 10be in soil profiles a global meta analysis abstract in order to assess current understanding of meteoric 10 be dynamics and distribution in terrestrial soils we assembled a database of all published meteoric 10 be soil depth profiles including 104 profiles from 27 studies in globally diverse locations collectively containing 679 individual measurements this allows for the systematic comparison of meteoric 10 be concentration to other soil characteristics and the comparison of profile depth distributions between geologic settings percent clay 9 be and dithionite citrate extracted al positively correlate to meteoric 10 be in more than half of the soils where they were measured but the lack of significant correlation in other soils suggests that no one soil factor controls meteoric 10 be distribution with depth dithionite citrate extracted fe and cation exchange capacity are only weakly correlated to meteoric 10 be percent organic carbon and ph are not significantly related to meteoric 10 be concentration when all data are complied the compilation shows that meteoric 10 be concentration is seldom uniform with depth in a soil profile in young or rapidly eroding soils maximum meteoric 10 be concentrations are typically found in the uppermost 20 cm in older more slowly eroding soils the highest meteoric 10 be concentrations are found at depth usually between 50 and 200 cm we find that the highest measured meteoric 10 be concentration in a soil profile is an important metric as both the value and the depth of the maximum meteoric 10 be concentration correlate with the total measured meteoric 10 be inventory of the soil profile in order to refine the use of meteoric 10 be as an estimator of soil erosion rate we compare near surface meteoric 10 be concentrations to total meteoric 10 be soil inventories these trends are used to calibrate models of meteoric 10 be loss by soil erosion erosion rates calculated using this method vary based on the assumed depth and timing of erosional events and on the reference data selected

tectonics fracturing of rock and erosion 1 we argue that by fracturing rock not by raising it relative to base level tectonics plays its most important role in causing rapid incision of valleys and rapid erosion of hillslopes tectonic deformation riddles the upper crust with fractures which not only provide avenues for water flow and thus promote weathering and further disintegration of rock but also fragment bedrock into debris that is readily extracted and transported by surface processes bends in active faults require straining of adjacent rock masses aftershocks that occur subsequent to slip on primary faults reflect penetrative brittle deformation of the upper crust at least some aftershocks must nucleate or lengthen cracks which contribute to the comminution of these rock masses scaling rules suggest that dimensions of ruptures for very small m 2 earthquakes can be meters or less the gutenberg richter recurrence relationship implies that such earthquakes are common as high magnification seismographs in low noise environments confirm moreover large differences among fault plane solutions for aftershocks show that the small faults on which they occur are not parallel to one another some faults must intersect thus the upper crust in tectonically active regions should be fragmented into blocks down to the scale of boulders or smaller dismembered rock arrives at the earth s surface already prepared to be transported away as a corollary both deeply exhumed lower crust and posttectonic igneous rock never deformed under brittle conditions and not deformed recently should be less susceptible to detachment and subsequent transport than fractured rock

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

mineral weathering and elemental transport during hillslope evolution at the susquehanna shale hills critical zone observatory located in the uplands of the valley and ridge physiographic province of pennsylvania the susquehanna shale hills critical zone observatory ssho is a tectonically quiescent first order catchment developed on shales of the silurian rose hill formation we used soil cores augered at the highest point of the watershed and along a subsurface water flowline on a planar hillslope to investigate mineral transformations and physical chemical weathering fluxes about 25 m of bedrock was also drilled to estimate parent composition depletion of carbonate at tens of meters of depth in bedrock may delineate a deep carbonate weathering front overlying this extending from 6 m below the bedrock soil interface up into the soil is the feldspar dissolution front in the soils depletion profiles for k mg si fe and al relative to the bedrock define the illite and chlorite reaction fronts when combined with a cosmogenic nuclide derived erosion rate on watershed sediments these depletion profiles are consistent with dissolution rates that are several orders of magnitudes slower for chlorite 1 5 10 17 mol m 2 s 1 and illite 2 9 10 17 mol m 2 s 1 than observed in the laboratory mineral reactions result in formation of vermiculite hydroxy interlayered vermiculite and minor kaolinite during weathering exchangeable divalent cations are replaced by al as soil ph decreases the losses of mg and k in the soils occur largely as solute fluxes in contrast losses of al and fe are mostly as downslope transport of fine particles physical erosion of bulk soils also occurs results from a steady state model demonstrate that physical erosion accounts for about half of the total denudation at the ridgetop and midslope positions chemical weathering losses of mg na and k are higher in the upslope positions likely because of the higher degree of chemical undersaturation in porewaters chemical weathering slows down in the valley floor and al and si even show net accumulation the simplest model for the hillslope that is consistent with all observations is a steady state clay weathering limited system where soil production rates decrease with increasing soil thickness

approaches to dynamic equilibrium in theoretical simulations of slope development the model slop3d is used to identify characteristic aspects of slope development under different conditions a series of slopes along the kall valley in the northern eifel is reproduced by a developmental sequence of model slopes the spatial and temporal variations of the components of slope development systems relief slope form weathering rates denudation rates are discussed by means of mass movement and wash denudation models the negative feedbacks between system components create a tendency towards the establishment of a dynamic equilibrium which is reached however only if the endogenic and exogenic conditions remain constant for the required relaxation time the latter is shown to be a function of slope length of the rate of uplift of the denudational process type and of the intensity of exogenic inputs e g precipitation varying rock resistance leads to the development of shield inselbergs only if the rate of denudation becomes higher than the maximum possible weathering rate of the resistant bedrock

coupling meteoric 10be with pedogenic losses of 9be to improve soil residence time estimates on an ancient north american interfluve we couple meteoric 10 be measurements with mass balance analysis of 9 be to estimate the soil residence time srt of a biogeomorphically stable ultisol in the southern piedmont physiographic region of the southeastern united states we estimate srt after correcting the meteoric 10 be inventory to account for observed 9 be losses which indicate that more than half of the 9 be weathered from primary minerals has been leached from the upper 18 3 m of the ultisol our estimates of minimum srt range between 1 3 1 4 ma and between 2 6 3 1 ma under high and low 2 0 and 1 3 10 6 atoms cm 2 yr 1 respectively estimates of 10 be delivery denudation rates of the physiographic region corroborate our estimates we redefine pedogenic time constraints in the southern piedmont and demonstrate that the assumption of complete meteoric 10 be retention in acidic soil systems cannot always be made the latter has far reaching consequences for soil sediment river and ocean research using meteoric 10 be

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

cooling of the bushveld complex south africa implications for paleomagnetic reversals igneous rocks record the direction of the earth s magnetic field as they cool through their curie temperature the mafic magmas of the 8 km thick bushveld complex of south africa took 65 k y to be emplaced 180 k y to solidify to 900 c and a further 500 k y for the entire intrusion to cool below 580 c the curie temperature of magnetite once solid the cooling of this intrusion occurred mainly from the top downward with slower cooling through its floor as a result the upper rocks cooled through their curie temperature before those at the base the portion 6 km below the upper contact was the last to reach the curie temperature thus the intrusion records a mainly top down sequence of three paleomagnetic reversals starting with n normal direction the last two are also recorded from the base of the mafic sequence upward as it cooled through 580 c later than the top the lateral variations in thickness of the bushveld complex are important in this interpretation because thinner sections cooled more quickly hence reversals do not always correlate with stratigraphy specific reversals provide a cooling marker horizon that may crosscut the stratigraphic layering the interpretation of the order and number of paleomagnetic reversals presented here differs from previous interpretations that envisage the oldest paleomagnetic directions to be recorded sequentially from the base upward and has implications for the interpretation of paleomagnetic results from all thick intrusions mafic and felsic

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

neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates abstract the persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution in the eastern north american appalachians this question is manifest in the outstanding problem of whether topographic relief is in a quasi equilibrium state decaying slowly over many millennia or whether relief has increased during the late cenozoic here we present quantitative geomorphic data from the nonglaciated portion of the susquehanna river drainage basin that provide insight into these end member models analysis of channel profiles draining upland catchments in the northern valley and ridge appalachian plateau blue ridge and piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300 600 m elevation but not systematically associated with transitions from weak to resistant substrate cosmogenic 10 be inventories of modern stream sediment indicate that erosion rates are spatially variable ranging from 5 30 m myr above knickpoints to 50 100 m myr below knickpoints overall channel gradients normalized for drainage area scale linearly with catchment averaged erosion rates collectively regionally consistent spatial relationships among erosion rate channel steepness and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with 100 150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization channel response timescales imply that the onset of relative base level change predates 3 5 ma and may have begun as early as 15 ma we suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of north america during the neogene

long term stability of global erosion rates and weathering during late cenozoic cooling reports that the geological record of erosion indicates a fourfold increase in global sedimentation rates during the past 5 million years merited a global explanation explanations offered include an increased rate of mountain formation and global cooling now jane willenbring and friedhelm von blanckenburg reanalyse original data sets and use ocean records of beryllium isotope ratios to obtain an indirect measure of past erosion rates and rock weathering they find no clear evidence either for an increase in global erosion or for a pulse of weathered material in the oceans during the past 12 million years they suggest that cenozoic global cooling must have some other cause and the mountain building that did occur had little effect on erosion or weathering flux globally accelerated uplift and global cooling have been suggested as possible causes for a fourfold increase in global sedimentation rates and by inference in erosion rates or weathering fluxes during the past 5 million years here proxy evidence is provided that indicates stable weathering fluxes in the late cenozoic era it is proposed that processes different from an increase in denudation caused cenozoic global cooling over geologic timescales co2 is emitted from the earth s interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial this balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions1 changes in this balance have been attributed to changes in topographic relief where varying rates of continental rock weathering and erosion1 2 are superimposed on fluctuations in organic carbon burial3 geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation1 2 4 widespread observations of a recent 0 5 myr fourfold increase in global sedimentation rates require a global mechanism to explain them4 5 6 accelerated uplift and global cooling have been given as possible causes2 4 6 7 but because of the links between rates of erosion and the correlated rate of weathering8 9 an increase in the drawdown of co2 that is predicted to follow may be the cause of global climate change instead2 however globally rates of uplift cannot increase everywhere in the way that apparent sedimentation rates do4 10 moreover proxy records of past atmospheric co2 provide no evidence for this large reduction in recent co2 concentrations11 12 here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record13 as evidence we recast the ocean dissolved 10be 9be isotope system as a weathering proxy spanning the past 12 myr ref 14 this proxy indicates stable weathering fluxes during the late cenozoic era the sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean we conclude that processes different from an increase in denudation caused cenozoic global cooling and that global cooling had no profound effect on spatially and temporally averaged weathering rates

long term kinematics and sediment flux of an active earthflow eel river california although earthfl ows are the dominant erosion mechanism in many mountainous landscapes estimates of long term earthfl ow driven sediment fl ux remain elusive because landslide displacement data are typically limited to contemporary time periods combining high resolution topography from airborne lidar light detection and ranging total station surveying orthorectifi ed historical aerial photographs and inventories of meteoric 10 be in soil pits we quantifi ed 150 years of slope movement on a 1 5 km long earthfl ow in the eel river catchment northern california united states using lidar derived topography we mapped the upper half of the earthfl ow into three distinct kinematic zones an upslope source area a long narrow transport zone and a mid slope compressional zone from our air photo analysis 1944 2006 average velocities are fastest in the transport zone 1 7 m a slowest in the source zone 1 m a and decrease monotonically over the past 30 years in all three zones meteoric 10 be inventories systematically increase with distance downslope of the source area consistent with the notion that the elongate transport zone acts like a relatively undeformed soil conveyor that can be used to quantify long term displacement because our 10 be derived transport zone velocity of 2 1 m a averages over the past 150 years pre 1944 velocities likely approached 2 5 m a suggesting that twentieth century land use practices have not increased rates of sliding although our results reveal a progressive decline in velocity that may refl ect exhaustion of readily mobilized source material velocities temporarily increased in the midtwentieth century due to major hydrologic events given an average velocity of 2 m a the kekawaka earthfl ow is defl ating its source area over 20 times faster than the regional erosion rate emphasizing the localized and vigorous role of active earthfl ows in landscape evolution

regolith production rates calculated with uranium series isotopes at susquehanna shale hills critical zone observatory abstract in the critical zone where rocks and life interact bedrock equilibrates to earth surface conditions transforming to regolith the factors that control the rates and mechanisms of formation of regolith defined here as material that can be augered are still not fully understood to quantify regolith formation rates on shale lithology we measured uranium series u series isotopes 238 u 234 u and 230 th in three weathering profiles along a planar hillslope at the susquehanna shale hills observatory ssho in central pennsylvania all regolith samples show significant u series disequilibrium 234 u 238 u and 230 th 238 u activity ratios range from 0 934 to 1 072 and from 0 903 to 1 096 respectively these values display depth trends that are consistent with fractionation of u series isotopes during chemical weathering and element transport i e the relative mobility decreases in the order 234 u 238 u 230 th the activity ratios observed in the regolith samples are explained by i loss of u series isotopes during water rock interactions and ii re deposition of u series isotopes downslope loss of u and th initiates in the meter thick zone of bedrock that cannot be augered but that nonetheless consists of up to 40 clay silt sand inferred to have lost k mg al and fe apparent equivalent regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m myr to 17 m myr with increasing regolith thickness from the ridge top to the valley floor with increasing distance from the ridge top toward the valley apparent equivalent regolith residence times increase from 7 kyr to 40 kyr given that the ssho experienced peri glacial climate 15 kyr ago and has a catchment wide averaged erosion rate of 15 m myr as inferred from cosmogenic 10 be we conclude that the hillslope retains regolith formed before the peri glacial period and is not at geomorphologic steady state both chemical weathering reactions of clay minerals and translocation of fine particles colloids are shown to contribute to mass loss of u and th from the regolith consistent with major element data at ssho this research documents a case study where u series isotopes are used to constrain the time scales of chemical weathering and regolith production rates regolith production rates at the ssho should be useful as a reference value for future work at other weathering localities

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

beryllium isotope geochemistry in tropical river basins abstract the distributions of beryllium 9 and beryllium 10 in rivers within the orinoco and amazon basins have been examined to extend our understanding of their geochemical cycles and to develop their use both in geochronometry and in studying erosional processes beryllium 9 the stable isotope is weathered from mineral lattices before entering the riverine dissolved or exchangeable phase the cosmogenic radioisotope 10be t 1 2 1 5 myr is produced primarily in the atmosphere and is brought into riverine systems via rainfall in dissolved or exchangeable form it may be used to examine the processes which affect beryllium partitioning between the dissolved and particulate phases ancillary data such as major ion distributions provide a basis for selecting regions in which riverine chemistry is dominated by a single geochemical process allowing examination of its effects on be distributions in isolation analyses of 9be in dissolved and suspended material from rivers with a wide range of chemical compositions indicate that its geochemistry is primarily controlled by two major factors 1 1 its abundance in the rocks of the watershed and 2 2 the extent of its adsorption onto particle surfaces the relative importance of these parameters in individual rivers is determined by the extent of interaction with flood plain sediments and the riverine ph this understanding of 9be geochemistry forms a basis for examination of the geochemical cycling of 10be in rivers which are dominated by interaction with sediments the riverine concentration of dissolved 10be is far lower than that in the incoming rainwater indicating that a substantial proportion of it is retained within the soils of the basin or is adsorbed onto riverine particles however in acidic rivers in which the stable dissolved be concentration is determined by the be level in the rocks of the drainage basin dissolved 10be has essentially the same concentration as in precipitation these observations imply that the soil column in such regions must be saturated with respect to 10be and that the ratio of the inventory to the flux does not represent an age as may be the case in temperate latitudes but rather a residence time

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

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

periglacial geomorphology of the appalachian highlands and interior highlands south of the glacial border a review abstract many features reported in the appalachian region have been assigned a paleoperiglacial origin based on field relationships and their similarities with analogs active in present day actuoperiglacial environments these forms include but are not limited to sorted and nonsorted varieties of patterned ground grezes litees block fields block slopes and block streams cryoplanation terraces and hillslope and river terrace landscapes although very small scale features generally less than 1 m in plan or section dimension and some larger forms on steep hillslopes are known to be at least sporadically active today the large scale features discussed here are interpreted as either inactive or truly fossil periglacial phenomena thus they hav implications for paleoclimatic reconstruction and significance as indicators of relative landscape stability since the time s of their development this paper briefly reviews the historical dimension of early researchs work present selected examples of recent results and gives authors conclusions

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

evolution of the bonneville shoreline scarp in west central utah comparison of scarp analysis methods and implications for the diffusion model of hillslope evolution abstract wave cut pluvial shoreline scarps are ideal natural experiments in hillslope evolution because the ages of these scarps are often precisely known and because they form with a range of heights alluvial textures and microclimates i e orientation previous work using midpoint slope methods on pluvial scarps in the basin and range concluded that scarp evolution is nonlinear and microclimatically controlled the purpose of this study was to further examine the influence of scarp height texture and microclimate in an attempt to calibrate a nonlinear model of scarp evolution to do this over 150 profiles of the bonneville shoreline in the adjacent snake and tule valleys west central utah were collected and analyzed by fitting the entire scarp profile to diffusion equation solutions taking into account uncertainty in the initial scarp angle in contrast to previous studies this analysis revealed no evidence for nonlinearity or microclimatic control to understand the reason for this discrepancy we undertook a systematic study of the accuracy of each scarp analysis method the midpoint slope inverse method was found to yield biased results with systematically higher diffusion ages for young tall scarps the slope offset method is unbiased but has limited resolution because it requires many scarp profiles to yield a single diffusion age a method that incorporates the full scarp profile and uncertainty in the initial scarp angle was found to be the most accurate technique the application of the full scarp method to the bonneville shoreline supports the use of a linear diffusion model for scarps up to 20 m in height scarp orientation had no discernable effect on diffusivity values soil texture was found to have a weak but significant inverse relationship with diffusivity values

uranium series comminution ages of continental sediments case study of a pleistocene alluvial fan obtaining quantitative information about the timescales associated with sediment transport storage and deposition in continental settings is important but challenging the uranium series comminution age method potentially provides a universal approach for direct dating of quaternary detrital sediments and can also provide estimates of the sediment transport and storage timescales the word comminution means to reduce to powder reflecting the start of the comminution age clock as reduction of lithic parent material below a critical grain size threshold of 50 mu m to test the comminution age method as a means to date continental sediments we applied the method to drill core samples of the glacially derived kings river fan alluvial deposits in central california sediments from the 45 m core have independently estimated depositional ages of up to 800 ka based on paleomagnetism and correlations to nearby dated sediments we characterized sequentially leached core samples both bulk sediment and grain size separates for u nd and sr isotopes grain size surface texture and mineralogy in accordance with the comminution age model where 234u is partially lost from small sediment grains due to alpha recoil we found that 234u 238u activity ratios generally decrease with age depth and specific surface area with depletions of up to 9percent relativemore to radioactive equilibrium the resulting calculated comminution ages are reasonable although they do not exactly match age estimates from previous studies and also depend on assumptions about 234u loss rates the results indicate that the method may be a significant addition to the sparse set of available tools for dating detrital continental sediments following further refinement improving the accuracy of the method requires more advanced models or measurements for both the recoil loss factor fa and weathering effects we discuss several independent methods for obtaining fa on individual samples that may be useful for future studies less

10be chronometry of bedrock to soil conversion rates abstract we report concentrations of cosmogenic 10 be t 1 2 1 5 10 6 yrs in soil excavated from a soil mantled hillslope in black diamond mines regional park contra costa county california the most striking features of the data are 1 the similarity in the downward decreasing trends of 10 be concentrations in two soil profiles collected 75 m apart 2 the coincidence in each soil profile of the soil bedrock interface as defined by visual inspection of soil pits and the level at which 10 be concentrations attain very low values 4 10 6 atoms g and 3 the extremely low 10 be concentrations in the underlying regolith 0 5 10 6 atoms gram the inventory of 10 be in these soils is low equivalent to about 6000 yrs of 10 be accumulation in a soil initially containing no 10 be on the basis of these measurements and with the aid of simple models of soil 10 be motions on the hillslope we conclude that 10 be loss from the surface is dominated by its removal in soil by creep we calculate local rates of bedrock to soil conversion of between 0 15 and 0 27 km 10 6 yrs comparing these with uplift rates determined for coastal regions of california indicates that soil creep alone is capable of removing soil from the local geomorphic system at a rate equivalent to the rate of uplift of much of the coast

regolith production and transport at the susquehanna shale hills critical zone observatory part 2 insights from meteoric 10be 1 regolith mantled hillslopes are ubiquitous features of most temperate landscapes and their morphology reflects the climatically biologically and tectonically mediated interplay between regolith production and downslope transport despite intensive research few studies have quantified both of these mass fluxes in the same field site here we present an analysis of 87 meteoric 10be measurements from regolith and bedrock within the susquehanna shale hills critical zone observatory ssho in central pennsylvania meteoric 10be concentrations in bulk regolith samples n 73 decrease with regolith depth comparison of hillslope meteoric 10be inventories with analyses of rock chip samples n 14 from a 24 m bedrock core confirms that 80 of the total inventory is retained in the regolith the systematic downslope increase of meteoric 10be inventories observed at ssho is consistent with 10be accumulation in slowly creeping regolith 0 2 cm yr 1 regolith flux inferred from meteoric 10be varies linearly with topographic gradient determined from high resolution light detection and ranging based topography along the upper portions of hillslopes at ssho however regolith flux appears to depend on the product of gradient and regolith depth where regolith is thick near the base of hillslopes meteoric 10be inventories at the north and south ridgetops indicate minimum regolith residence times of 10 5 3 7 and 9 1 2 9 ky respectively similar to residence times inferred from u series isotopes in ma et al 2013 the combination of our results with u series derived regolith production rates implies that regolith production and erosion rates are similar to within a factor of two on ssho hillcrests

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

lithofacies of the silurian keefer sandstone east central appalachian basin usa abstract fourteen lithofacies of the keefer sandstone in the area of northeastern west virginia and western maryland were identified depositional environments of the lithofacies include storm dominated marine shelf basin barrier island and backbarrier tidal flat and lagoon coastal lithofacies document a dominant basinward progradation with some sea level rise which placed backbarrier lithofacies above barrier island lithofacies shelf lithofacies as stacked coarsening upward sequences document as many as four fluctuations within the major progradation coarsening upward sequences are typically capped by transgressive sands which represent material eroded from relatively landward environments and transported basinward during coastal retreat deposition of cycles within the keefer occurred under conditions of tectonic quiescence dominant steady or falling sea level followed by rise in sea level and in a climate which was warm and humid

natural streams and the legacy of water powered mills gravel bedded streams are thought to have a characteristic meandering form bordered by a self formed fine grained floodplain this ideal guides a multibillion dollar stream restoration industry we have mapped and dated many of the deposits along mid atlantic streams that formed the basis for this widely accepted model these data as well as historical maps and records show instead that before european settlement the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon subsequently 1 to 5 meters of slackwater sedimentation behind tens of thousands of 17th to 19th century milldams buried the presettlement wetlands with fine sediment these findings show that most floodplains along mid atlantic streams are actually fill terraces and historically incised channels are not natural archetypes for meandering streams

bedrock erosion by root fracture and tree throw a coupled biogeomorphic model to explore the humped soil production function and the persistence of hillslope soils 1 in 1877 g k gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker subsequent analyses of this humped functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil to explore this issue we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw the coupled biogeomorphic model combines data on conifer population dynamics rootwad volumes tree throw frequency and soil creep from the pacific northwest usa although not hardwired into the model a humped relationship emerges between bedrock erosion and soil thickness the magnitudes of the predicted bedrock erosion rates and their functional dependency on soil thickness are consistent with independent field measurements from a coniferous landscape in the region imposed perturbations of soil erosion during model runs demonstrate that where bedrock weathering is episodic and localized hillslope soils do not exhibit runaway thinning or thickening the pit and mound topography created by tree throw produces an uneven distribution of soil thicknesses across a hillslope thus although episodes of increased erosion can lead to temporary soil thinning and even the exposure of bedrock patches local areas of thick soils remain these soil patches provide habitat for trees and serve as nucleation points for renewed bedrock erosion and soil production model results also suggest that where tree throw is a dominant weathering process the initial mantling of bedrock is not only a vertical process but also a lateral process soil mounds created by tree throw flatten over time spreading soil over bedrock surfaces

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

comment on testing emplacement models for the rustenburg layered suite of the bushveld complex with numerical heat flow models and plagioclase geospeedometry by s j robb and j e mungal earth planet sci lett 534 2020 116084

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

fully coupled approach to modeling shallow water flow sediment transport and bed evolution in rivers 1 our ability to predict complex environmental fluid flow and transport hinges on accurate and efficient simulations of multiple physical phenomenon operating simultaneously over a wide range of spatial and temporal scales including overbank floods coastal storm surge events drying and wetting bed conditions and simultaneous bed form evolution this research implements a fully coupled strategy for solving shallow water hydrodynamics sediment transport and morphological bed evolution in rivers and floodplains pihm hydro and applies the model to field and laboratory experiments that cover a wide range of spatial and temporal scales the model uses a standard upwind finite volume method and roe s approximate riemann solver for unstructured grids a multidimensional linear reconstruction and slope limiter are implemented achieving second order spatial accuracy model efficiency and stability are treated using an explicit implicit method for temporal discretization with operator splitting laboratory and field scale experiments were compiled where coupled processes across a range of scales were observed and where higher order spatial and temporal accuracy might be needed for accurate and efficient solutions these experiments demonstrate the ability of the fully coupled strategy in capturing dynamics of field scale flood waves and small scale drying wetting processes

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

10be concentrations and the long term fate of particle reactive nuclides in five soil profiles from california concentration depth profiles of cosmic ray produced 10 be t 1 2 1 5m y have been measured by accelerator mass spectrometry in five soil profiles these measurements were made in an effort 1 to understand the retentivity of soil surfaces for particle reactive tracers depositing from the atmosphere on time scales of 10 4 10 6 years and 2 to explore the application of 10 be as a chronometer of geomorphic surface age the profiles sampled are from two wave cut terraces located near mendocino california a table mountain top and an alluvial fan both located near friant california the ages of the mendocino terraces are inferred to be 1 5 10 5 years based on amino stratigraphic correlations and models of terrace evolution those of the table mountain top and alluvial fan are 9 5 10 6 years and 6 0 10 5 years respectively based on k ar analyses all the surfaces sampled are nearly flat and exhibit few erosional features in addition to 10 be we measured 210 pb 239 240 pu and 7 be to ascertain the retentivity of the soils for particle reactive nuclides and to assess the present day delivery rate of nuclides from the atmosphere the 7 be inventory is 4 0 dpm cm 2 similar to those observed at nearby locations the inventories of 210 pb and pu isotopes conform to those predicted from model calculations and suggest that the soil surfaces sampled retain the entire burden of particle reactive nuclides delivered to them over short time scales 100 years the 10 be concentrations in the sample range between 0 2 and 7 10 8 atoms g soil and show strong correlations with leachable fe and or al the inventory of 10 be in the soil domain sampled is 1 2 orders of magnitude lower than that expected from the geological age of the surface and an average delivery rate of 10 be from the atmosphere 5 2 10 5 atoms cm 2 yr the low inventory of 10 be is attributed to its loss from the soil domain sampled by solution transport based on a simple model type calculation with a first order removal process for 10 be the residence time of 10 be in the soil domains sampled is determined to be of the order of 10 4 years the low residence time of 10 be in the soil domains sampled requires that it be found either deeper in the regolith or in ground waters in either case the application of 10 be as a chronometer of geomorphic surface age is severely constrained however the study of 10 be in soils provides the only entry into the long term 10 4 10 6 years behavior of particle reactive nuclides in soils and hence could be important for understanding the behavior of analogous nuclides introduced into soils by natural and anthropogenic processes

emplacement and crystallization time for the bushveld complex the bushveld complex formed by the crystallization of successive basaltic magmatism may be of the order of several million years for example the columbia river basalts hooper injections of magma which were sufficiently closely spaced in time that each previous magma had not cooled and differentiated 1988 were erupted in the period 17 12 ma with minor eruptions for a further 5 my although most outpouring significantly before the addition of the next one to constrain the emplacement and crystallization times a thermal model is presented occurred within the first 2 my it is now recognized that large intrusions were not emplaced in a single pulse but which permits the investigation of the rate of cooling of magma in an intrusion repeatedly subjected to magma addition and subresult from multiple magma injection the question is how rapidly were magma chambers such as the bc traction such modelling indicates that magmas injected into the bushveld complex were emplaced within 75 000 years at that filled and how much magma was involved answers are relevant to the dynamics of melt production storage and time injection into the complex ceased the volume of rock in the eastern and western limbs is 370 000 600 000 km however transport in the mantle and crust this paper describes a thermal modelling technique not previously applied a quantitative evaluation of the cr budget in the formation of chromitite layers indicates that large volumes of magma cannot be to magma chambers which can be used to analyse this process and to obtain an estimate of the emplacement accounted for in the preserved rock sequence similarly an evaluation of the incompatible trace element abundances such as those for zr time to present this model it is necessary to discuss the stratigraphy size and connectivity of the different limbs and k suggests that the chamber was open and that large volumes of differentiated magma escaped the volume of magma therefore of the bushveld complex and to consider the extent of tapping of the magma chamber as well as its filling greatly exceeded the preserved volume of cumulate rocks giving an estimated magma volume of over 1 10 km an average the term bushveld complex has been given several meanings in the literature and according to the south emplacement rate of 13 km year is indicated by these calculations african commission on stratigraphy 1980 includes not only the ultramafic mafic layered rocks but also the sills beneath the intrusion volcanic rocks which pre date the

geochemical behaviors of different element groups during shale weathering at the susquehanna shale hills critical zone observatory major and trace element concentrations were measured in bedrock regolith and stream sediments from a first order catchment developed entirely on grey shale in central pennsylvania usa these elements can be classified into five major groups based on statistical data analysis the presence of different elemental groups is due to the mineralogical origin cycling processes and geochemical properties of these elements during soil formation a better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in critical zone processes

uranium series isotopes in river materials insights into the timescales of erosion and sediment transport abstract the uranium series isotope signatures of the suspended and dissolved load of rivers have emerged as an important tool for understanding the processes of erosion and chemical weathering at the scale of a watershed these signatures are a function of both time and weathering induced fractionation between the different nuclides provided appropriate models can be developed they can be used to constrain the residence time of river sediment this chronometer is triggered as the bedrock starts weathering and the inferred timescale encompasses the residence time in the weathering profile storage in temporary sediment deposits e g floodplain and transport in the river this approach has been applied to various catchments over the past five years showing that river sediments can reside in a watershed for timescales ranging from a few hundreds of years iceland to several hundreds of thousands of years lowlands of the amazon various factors control how long sediment resides in the watershed the longest residence times are observed on stable cratons unaffected by glacial cycles or more generally climate variability and human disturbance shorter residence times are observed in active orogens andes or fast eroding recently glaciated catchments iceland in several cases the residence time of suspended sediments also corresponds to the time since the last major climate change the u series isotope composition of rivers can also be used to predict the river sediment yield assuming steady state erosion is reached by comparing this estimate with the modern sediment yield obtained by multi year sediment gauging it is clear that steady state is seldom reached this can be explained by climate variability and or human disturbance steady state is reached in those catchments where sediment transport is rapid iceland or where the region has been unaffected by climate change and or human disturbance u series are thus becoming an important tool to study the dynamics of erosion

a high resolution late quaternary upwelling record from the anoxic cariaco basin venezuela results are presented of a high resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the cariaco basin in the southern caribbean sea the cariaco basin is a small anoxic marine basin on the northern continental margin of venezuela in an area today characterized by both seasonal trade wind induced upwelling and pronounced dry and wet seasons our data indicate that large changes in the intensity of upwelling and hence trade wind strength occurred in this region during the last glacial interglacial transition and throughout the holocene during the last glacial lowstand of sea level the cariaco basin was effectively isolated from the open caribbean along its northern margin by the then largely emergent tortuga bank oxic conditions existed in the deep cariaco basin at this time and surface productivity was low about 12 600 years ago the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the laurentide ice sheet into the gulf of mexico strong upwelling between 12 600 and about 10 000 years ago may be related to intensified trade winds resulting in part from cooler sea surface temperatures in the caribbean and gulf of mexico after about 10 000 years ago upwelling intensity was reduced though highly variable a preliminary frequency domain analysis of the holocene portion of the cariaco basin time series suggests that solar forcing may explain a significant component of the century scale variability observed in the record of upwelling and trade wind strength

testing emplacement models for the rustenburg layered suite of the bushveld complex with numerical heat flow models and plagioclase geospeedometry abstract conventional models of the genesis of the rustenburg layered suite rls of the bushveld complex postulate that it is the product of a single multiply replenished magma chamber that cooled as a single massive unit i e a monolithic magma chamber this concept has been challenged by alternative hypotheses involving out of sequence emplacement of some of its major layers as sills both scenarios have partial support from high precision u pb geochronological data to test these contradictory hypotheses new zircon geothermometric data and compositional data for plagioclase from the upper critical zone are presented and the available geochronological data are tested against the predictions of the thermal evolution of the entire rls for both emplacement and cooling scenarios crystallization temperatures of zircon within units of the upper critical zone were estimated using ti in zircon thermometry and range between 799 45 c and 865 64 c the data are used in conjunction with a detailed numerical model of heat flow in the bushveld complex that is used to approximate the duration and extent of thermal perturbations felt throughout the system and delimit the time intervals during which zircon crystals could have grown at the measured crystallization temperatures the results show that prolonged cooling histories 1 myr that would be experienced near the centre of a large slowly cooled plutonic magma chamber would erase signs of plagioclase zoning at 4 kbar and moderate f h 2 o however plagioclase crystals with zoning profiles spanning at least 10 mole an are common in the upper critical zone in contrast emplacement of the major units of the rls at widely separated intervals as recorded by the existing high precision u pb dataset would impose transient thermal effects on the system against a backdrop of generally much lower ambient temperatures throughout its evolution in this scenario apparent ages of zircon crystals would record the time of cooling through temperatures near the water saturated biotite granite solidus corresponding to the final intercumulus mineral assemblage in both mafic and ultramafic macrolayers subsequent reheating of these rocks would be unable to reset primary zircon crystallization dates but might in some examples result in some amount of remelting or regrowth of zircon comparison of the evolving temperature fields of the two types of emplacement and cooling histories shows that the existing geochronological data and preservation of plagioclase zoning are consistent with out of sequence emplacement and rapid cooling of individual ultramafic sills into previously solidified lithologies of the rls but not with the conventional view of a single monolithic magma body

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

detection of erosion events using10be profiles example of the impact of agriculture on soil erosion in the chesapeake bay area u s a 10be concentration total carbon and grain size were measured in cores collected in undisturbed estuarine sediments of three tributaries of the chesapeake bay these cores were previously studied by davis 1 and brush 2 3 for pollen content age and sedimentation rate in this work we compare the results obtained for these various analyses in the cores we observed two increases in10be concentration concomitant with two major changes in the pollen composition of the sediments these two pollen changes each correspond to well dated agricultural horizons reflecting different stages in the introduction of european farming techniques 2 in the chesapeake bay area the agricultural development associated with forest clearing appears to have triggered the erosion transport and sedimentation into the river mouths of large quantities of10be rich soils this phenomenon explains the observed rise in the sedimentation rate associated with increases in agricultural land use