grain size dependent concentration of cosmogenic 10be and erosion dynamics in a landslide dominated himalayan watershed for documenting recent or late quaternary erosion rates at the scale of a small watershed or even an entire mountain range the use of in situ terrestrial cosmogenic nuclides tcn such as 10be in river sediments has become widespread over the last decade in mountainous settings however landslides may induce a two fold complication in the cosmogenic nuclide budget first they may episodically deliver large amounts of sediment with low tcn concentrations to the river channel second they may generate a grain size concentration dependence in these sediments however studies that have explored grain size dependence in landslide dominated areas have reached differing conclusions and the underlying mechanisms remain poorly understood the present study focuses on the khudi khola river basin a small drainage basin in the central himalayas the area is characterized by steep slopes heavy rainfall and high sediment production rates importantly the watershed contains a large area of active landsliding in situ 10be was analyzed in sediments of grain sizes ranging from 75 m to 4 cm collected from five locations upstream downstream and in the small tributaries which drain the landslides in all sampling locations including those situated upstream of the landslides the finest grains 75 250 m are two to four times more concentrated in 10be than the largest clasts 4 7 mm we developed a numerical slope model which includes a low level of background soil erosion and episodic denudation from large mass wasting events we then introduced a coarsening of average grain size with soil depth to the model our simulation shows that the data available for this valley are compatible with a scenario in which landslides deliver coarse grains to the channel that are less concentrated in tcn and have deeper provenance best fit estimates of the model parameters suggest recurrence times of 3000 to 9000 years for a major landslide on the same slope and mean long term landslide denudation rates of 1 7 to 4 7 mm yr 1 a negative correlation between tcn concentration and grain size is also observed directly upstream and 5 km downstream of the landsliding area suggesting that nearly all of the sediment carried by the river is derived from ancient landslides while almost no sediment is supplied by erosion of soil mantled slopes despite these complications apparent denudation rates directly derived from the tcn concentrations and from previously published data in the region are all on the same order of magnitude around 2 mm yr 1 however a factor of three variability remains between the different studies depending on the location the year of sampling and the analyzed grain size fraction thus although tcn derived average denudation rates provide a useful first order estimate even in fast eroding terrains dominated by landslides caution should be applied when using quantitative results in such settings

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

kinetically limited weathering at low denudation rates in semiarid climatic conditions biogeochemical cycling within the critical zone depends on the interactions between minerals and fluids controlling chemical weathering and physical erosion rates in this study we explore the role of water availability in controlling soil chemical weathering in semiarid climatic conditions weathering rates and intensities were evaluated for nine soil profiles located on convex ridge crests of three mountain ranges in the spanish betic cordillera we combine a geochemical mass balance with 10be cosmogenic nuclides to constrain chemical weathering intensities and long term denudation rates as such this study presents new data on chemical weathering and 10be derived denudation for understudied semiarid climate systems in the betic cordillera chemical weathering intensities are relatively low 5 to 30 of the total denudation of the soil and negatively correlated with the magnitude of the water deficit in soils chemical mass losses are inversely related to denudation rates 14 109 mm kyr and positively to soil thickness 14 58 cm these results are consistent with kinetic limitation of chemical weathering rates a worldwide compilation of chemical weathering data suggests that soil water balance may regulate the coupling between chemical weathering and physical erosion by modulating soil solute fluxes therefore future landscape evolution models that seek to link chemical weathering and physical erosion should include soil water flux as an essential driver of weathering

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

comparison of slope estimates from low resolution dems scaling issues and a fractal method for their solution five different algorithms for calculating slope from digital elevation models dems have been compared from regional to global scales though different methods produce different results the most significant outcome is that slope varies inversely with the dem grid size thus slopes estimated from coarse resolution data can be considered to produce significant underestimates of the true slope a fractal theory is adapted to solve this problem the variogram technique for the definition of fractal parameters is demonstrated to provide a relationship between slope and the spatial resolution of measurement the variation of fractal parameters is discussed at various scales and a model is developed to estimate the high resolution slope based on the coarse resolution dem by using fractal parameters the fractal parameters are estimated from the standard deviation of elevation in a 3 3 window of the dem to account for local variability in the surface standard deviation of elevation is found to be the most invariant property of different scale dems of the same area the model is validated using different resolution dems in southern spain and it is used to estimate the high resolution slope values at global scales based on a coarse resolution dem the slopes estimated using the technique outlined are a significant improvement on those estimated directly from the coarse resolution data slopes estimated in this way allow the more effective use of available coarse resolution data in regional and global scale modelling studies copyright 1999 john wiley sons ltd

deciphering the driving forces of erosion rates on millennial to million year timescales in glacially impacted landscapes an example from the western alps in many regions tectonic uplift is the main driver of erosion over million year myr timescales but climate changes can markedly affect the link between tectonics and erosion causing transient variations in erosion rates here we study the driving forces of millennial to myr scale erosion rates in the french western alps as estimated from in situ produced cosmogenic 10be and a newly developed approach integrating detrital and bedrock apatite fission track thermochronology millennial erosion rates from 10be analyses vary between 0 27 and 1 33 m kyr similar to rates measured in adjacent areas of the alps significant positive correlations of millennial erosion rates with geomorphic measures in particular with the lgm ice thickness reveal a strong transient morphological and erosional perturbation caused by repeated quaternary glaciations the perturbation appears independent of myr scale uplift and erosion gradients with the effect that millennial erosion rates exceed myr scale erosion rates only in the internal alps where the latter are low 0 4 km myr these areas moreover exhibit channels that clearly plot above a general linear positive relation between myr scale erosion rates and normalized steepness index glacial erosion acts irrespective of rock uplift and thus not only leads to an overall increase in erosion rates but also regulates landscape morphology and erosion rates in regions with considerable spatial gradients in myr scale tectonic uplift our study demonstrates that climate change e g through occurrence of major glaciations can markedly perturb landscape morphology and related millennial erosion rate patterns even in regions where myr scale erosion rates are dominantly controlled by tectonics

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

sedimentation under deep sea storms fast currents high concentrations of suspended sediment and grooved mud beds are associated with erosion in frequent abyssal storms where a fast deep mean flow is augmented or reversed by intense intermittent currents this occurs about 5 km below the gulf stream or its rings the waning phase of a storm results in development of bedforms and rapid deposition of a mud blanket several other regions of the world ocean display evidence of abyssal storm activity

effects of terrain smoothing on topographic shielding correction factors for cosmogenic nuclide derived estimates of basin averaged denudation rates estimation of spatially averaged denudation rates from cosmogenic nuclide concentrations in sediments depends on the surface production rates the scaling methods of cosmic ray intensities and the correction algorithms for skyline snow and vegetation shielding used to calculate terrestrial cosmogenic nuclide production while the calculation of surface nuclide production and application of latitude altitude and palaeointensity scaling algorithms are subjects of active research the importance of additional correction for shielding by topographic obstructions snow and vegetation is the subject of ongoing debate the derivation of all additional correction factor for skyline shielding for large areas is still problematic one important issue that has yet to he addressed is the effect of the accuracy and resolution of terrain representation by a digital elevation model dem on topographic shielding collection factors topographic metrics scale with the resolution of the elevalion data and terrain smoothing has a potentially large effect on the correction of terrestrial cosmogenic nuclide production rates for skyline shielding for rough high relief landscapes the effect of terrain smoothing call easily exceed analytical errors and should be taken into account here we demonstrate the effect of terrain smoothing on topographic shielding correction factors for various topographic settings and introduce an empirical model for the estimation of topographic shielding factors based on landscape metrics copyright c 2008 john wiley and sons ltd

model for turbidite to contourite continuum and multiple process transport in deep marine settings examples in the rock record abstract petrological analysis of geological sections in st croix in the caribbean the niesenflysch in switzerland and the annot sandstone in the french maritime alps sheds light on multiple process transport in deep marine settings a model depicting a turbidite to contourite continuum of stratal types is applied to these three rock units recognition of a diverse suite of bedforms coupled with analysis of paleocurrents helps to better interpret depositional origin and basin paleogeography the st croix strata record emplacement by gravity flows and subsequently by bottom currents flowing parallel to the base of slope these sediments accumulated on a lower slope apron a niesenflysch section in the swiss alps west of adelboden includes turbidites which were deposited at fairly regular intervals beyond the base of slope in a setting more distal than that of the st croix sequences most of these turbidites appear to have been partially reworked by bottom currents related to basin circulation or to density flows from the basin margins in the annot sandstone reworked turbidites termed transitional variants and packets of entirely rippled strata are observed in submarine fan and slope sequences in the peira cava area in contrast to those in st croix and the niesenflysch the current emplaced deposits of the annot sandstone are directly associated with fan valley deposits such rippled strata in channels are deposits of gravity flow origin which were subsequently reworked downslope by currents generated by successive gravity flows they also occur on levees by overbank flow consideration of multiple process transport is of special help to interpret sections which are poorly exposed or which can be examined in cores or which are located in sequences that have been highly deformed structurally

long term soil erosion derived from in situ 10be and inventories of meteoric 10be in deeply weathered soils in southern brazil abstract meteoric 10 be is commonly used as a geochemical tracer of soil erosion and regolith residence time over long time scales 10 3 yr the acidic conditions of tropical soils are less favorable for meteoric 10 be retention and make a translation of meteoric 10 be inventories into surface erosion rates complex in this empirical study we evaluate the potential loss of meteoric 10 be in the weathering zone along a toposequence in southern brazil three regolith profiles were sampled to explore the mobility of be in the soil system the sequential chemical extractions of four reactive fractions indicate that the amorphous oxy hydroxide and crystalline oxide fractions are the main carriers of meteoric 10 be our data from the brazilian toposequence reveal significantly higher inventories of meteoric 10 be in the slope concavities compared to the upslope positions this demonstrates that chemical leaching and deep percolation of meteoric 10 be within the soil profile leads to vertical and lateral redistribution of meteoric 10 be across the hillslope our data show that more than 50 of the delivered meteoric 10 be is leached from the upslope regolith profiles after correcting the inventories for incomplete retention of meteoric 10 be surface erosion rates are derived for the slope convexities upslope erosion rates are below 5 mm kyr and agree with the in situ 10 be derived denudation rates our results suggest that soil and sediment fluxes can accurately be derived from meteoric 10 be inventories in well developed soils when the meteoric 10 be mobility is constrained using differential mass balances

erosion of the rwenzori mountains east african rift from in situ produced cosmogenic10be 1 high relief and steep topography are thought to result in high erosion rates in the rwenzori mountains of the albert rift east africa where more than 3 km of relief have formed during uplift of the rwenzori fault block overall low denudation rates prevail we measured in situ derived cosmogenic denudation rates of 28 2 to 131 mm kyr in mountainous catchments and rates of 7 8 to 17 7 mm kyr on the adjacent low relief east african plateau these rates are roughly an order of magnitude lower than in other settings of similar relief we present an extensive geomorphological analysis and find that denudation rates are positively correlated with relief hillslope gradient and channel steepness indicating that river incision controls erosional processes in most upper headwater reaches above quaternary ela levels 4500 m a s l glacial imprinting inherited from several older and recent minor glaciation stages prevails in regions below 4500 m a s l however mild climatic conditions impede frost shattering favor dense vegetation and minimize bare rock areas and associated mass wasting we conclude that erosion of the rwenzori mountains is significantly slower than corresponding rates in other mountains of high relief due to a combination of factors extremely dense mountain cloud forest vegetation high rock strength of gneiss and amphibolite lithologies and low internal fracturing due to the extensional tectonic setting this specific combination unique to this extensional tropical setting leads to unexpected low erosion rates that cannot outpace post pliocene ongoing rock uplift of the rwenzori fault block

10be derived himalayan denudation rates and sediment budgets in the ganga basin abstract the himalayas represent the archetype of mountain building due to active continental collision and are considered in many studies as the locus of intense interactions between climate denudation and tectonics estimates of modern denudation rates across the entire range remain however relatively sparse in this study in situ produced cosmogenic 10 be concentrations were measured in detritic quartz in order to determine basin scale denudation rates for the central part of the himalayan range river sand was sampled over several years in the main trans himalayan rivers from the himalayan front to the ganga outlet in bangladesh the calculated 10 be denudation rates of the trans himalayan river basins range from 0 5 to 2 4 mm yr 1 average 1 3 mm yr 1 and vary by up to a factor of 3 between sampling years these denudation rates strongly contrast with the 0 007 mm yr 1 denudation rate of southern tributary basins draining the indian craton this work also shows that in the ganga basin no systematic evolution of average 10 be concentrations is observed during floodplain transfer implying that distal samples can be used to estimate the integrated denudation rate of the whole central himalayan range samples from the ganga in bangladesh display remarkably low variability in 10 be concentration implying an average himalayan denudation rate of 1 0 1 1 mm yr 1 however within the floodplain several samples suggest a recent perturbation of sediment transport dynamics with a recent increase in the relative sediment contribution from southern tributaries the himalayan sediment flux deduced from the 10 be denudation rate of the range is 610 230 mt yr 1 this flux is consistent within uncertainty with sediment fluxes derived from sediment gauging the similarity of the two flux estimates suggests that himalayan erosion fluxes have remained stable over the last centuries even if the large uncertainties associated with each method hamper more precise assessments

middle palaeozoic thrusting in the eastern lachlan fold belt southeastern australia abstract early to middle palaeozoic clastic and volcanic strata in the goulburn bungonia region 150 km southwest of sydney are divided by the n trending yarralaw fault into two domains in the western domain major e w shortening formed folds axial planar cleavage and w dipping contraction faults in all pre upper devonian units this deformation formed an anticlinorium cored by a w dipping thrust system with an overturned e younging limb in the eastern domain upright flattened chevron folds occur in ordovician strata with stratal repetition along steep contraction faults spaced at intervals of 1 km or less zones of tectonic melange occur in the hangingwalls of these faults and have a well developed scaly fabric with a steeply plunging striation overprinting a bedding parallel cleavage in mudstone in interbedded silurian shale and limestone a classical stair step trajectory is recognized for the frome hill fault which duplicates the succession and has undergone back rotation to its present steep dip overall thrusting progressed from east to west with deformation in the eastern domain pre dating intrusion of the early devonian marulan batholith whereas farther west deformation continued into the middle devonian the folds and thrusts in the goulburn bungonia region are part of a major fold thrust zone that extends throughout the eastern lachlan fold belt and which was formed in the middle silurian to middle devonian during a period of plate convergence between gondwana and the palaeo pacific ocean the fold thrust zone is inferred to have an arc frontal arc setting above a w dipping subduction zone and the deformation relates to underthrusting of an allochthonous terrane with major shortening in the hangingwall block

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

the influence of bedrock orientation on the landscape evolution surface morphology and denudation 10be at the niesen switzerland landscape evolution and surface morphology in mountainous settings are a function of the relative importance between sediment transport processes acting on hillslopes and in channels modulated by climate variables the niesen nappe in the swiss penninic prealps presents a unique setting in which opposite facing flanks host basins underlain by identical lithologies but contrasting litho tectonic architectures where lithologies either dip parallel to the topographic slope or in the opposite direction i e dip slope and non dip slope the north western facing diemtigen flank represents such a dip slope situation and is characterized by a gentle topography low hillslope gradients poorly dissected channels and it hosts large landslides in contrast the south eastern facing frutigen side can be described as non dip slope flank with deeply incised bedrock channels high mean hillslope gradients and high relief topography results from morphometric analysis reveal that noticeable differences in morphometric parameters can be related to the contrasts in the relative importance of the internal hillslope channel system between both valley flanks while the contrasting dip orientations of the underlying flysch bedrock has promoted hillslope and channelized processes to contrasting extents and particularly the occurrence of large landslides on the dip slope flank the flank averaged beryllium 10 10be derived denudation rates are very similar and range between 0 20 and 0 26 mm yr 1 in addition our denudation rates offer no direct relationship to basin s slope area steepness or concavity index but reveal a positive correlation to mean basin elevation that we interpret as having been controlled by climatically driven factors such as frost induced processes and orographic precipitation our findings illustrate that while the landscape properties in this part of the northern alpine border can mainly be related to the tectonic architecture of the underlying bedrock the denudation rates have a strong orographic control through elevation dependent mean annual temperature and precipitation

transient river response captured by channel steepness and its concavity mountain rivers draining tropical regions are known to be great conveyor belts carrying efficientlymore than half of the global sediment flux to the oceans many tropical mountain areas are located in tectonically active belts where the hillslope and stream channel morphology are rapidly evolving in response to changes in base level here we report basin wide denudation rates for an east west transect through the tropical andes hillslope and channel morphology vary systematically fromeast towest reflecting the transition from high relief strongly dissected topography in the escarpment zones into relatively low relief topography in the inter andean valley the spatial pattern of differential denudation rates reflects the transient adjustment of the landscape to rapid river incision following tectonic uplift and river diversion in the inter andean valley upstream of the wave of incision slopes and river channels display a relatively smooth concave up morphology and denudation rates time scale of 104 105 a are consistently low 3 to 200 mm ka in contrast slopes and river channels of rejuvenated basins draining the eastern cordillera are steep to very steep and the studied drainage basins show a wide range of denudation rate values 60 to 400 mm ka that increase systematically with increasing basin mean slope gradient channel steepness and channel convexity drainage basins that are characterised by strong convexities in their river longitudinal profiles systematically have higher denudation rates as such this is one of the first studies that provides field based evidence of a correlation between channel concavity and basin mean denudation rates consistent with process based fluvial incision models

differences in topographic characteristics computed from 100 and 1000 m resolution digital elevation model data topographic characteristics computed from 100 and 1000 m resolution digital elevation model dem data are compared for 50 locations representing varied terrain in the conterminous usa the topographic characteristics are three parameters used extensively in hydrological research and modelling slope s specific catchment area as and a wetness index computed as the logarithm of the specific catchment area divided by slope ln as s slope values computed from 1000 m dems are smaller than those computed from 100 m dems specific catchment area and the wetness index are larger for the 1000 m dems compared with the 100 m dems most of the differences between the 100 and 1000 m resolution dems can be attributed to terrain discretization effects in the computation of the topographic characteristics and are not the result of smoothing or loss of terrain detail in the coarse data in general the terrain discretization effects are greatest on flat terrain with long length scale features and the smoothing effects are greatest on steep terrain with short length scale features for the most part the differences in the average values of the topographic characteristics computed from 100 and 1000 m resolution dems are predictable that is biases in the mean values for the characteristics computed from a 1000 m dem can be corrected with simple linear equations copyright 2000 john wiley sons ltd

erosion of an ancient mountain range the great smoky mountains north carolina and tennessee analysis of 10be and 26al in bedrock n 10 colluvium n 5 including grain size splits and alluvial sediments n 59 including grain size splits coupled with field observations and gis analysis suggest that erosion rates in the great smoky mountains are controlled by subsurface bedrock erosion and diffusive slope processes the results indicate rapid alluvial transport minimal alluvial storage and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes spatially homogeneous erosion rates of 25 30 mm ky 1 are calculated throughout the great smoky mountains using measured concentrations of cosmogenic 10be and 26al in quartz separated from alluvial sediment 10be and 26al concentrations in sediments collected from headwater tributaries that have no upstream samples n 18 are consistent with an average erosion rate of 28 8 mm ky 1 similar to that of the outlet rivers n 16 24 6 mm ky 1 which carry most of the sediment out of the mountain range grain size specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones the difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains large sandstone clasts disaggregate into sand size grains rapidly during weathering and downslope transport thus only clasts from the lower parts of slopes reach the streams 26al 10be ratios do not suggest significant burial periods for our samples however alluvial samples have lower 26al 10be ratios than bedrock and colluvial samples a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down slope transport the results confirm some of the basic ideas embedded in davis geographic cycle model such as the reduction of relief through slope processes and of hack s dynamic equilibrium model such as the similarity of erosion rates across different lithologies comparing cosmogenic nuclide data with other measured and calculated erosion rates for the appalachians we conclude that rates of erosion integrated over varying time periods from decades to a hundred million years are similar the result of equilibrium between erosion and isostatic uplift in the southern appalachian mountains

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

frost cracking control on catchment denudation rates insights from in situ produced 10be concentrations in stream sediments ecrins pelvoux massif french western alps the potential tectonic and climatic controls on erosion rates in the european alps and other mountain belts remain strongly debated we have quantified denudation rates at catchment scales using in situ produced cosmogenic nuclides 10be in stream sediments sampled at the outlets of twelve variously sized 27 1072 km2 catchments of the ecrins pelvoux massif french western alps with average elevations ranging from 1700 to 2800 m spatially averaged denudation rates corrected for potential shielding by little ice age glaciers vary from 0 27 0 05 to 1 07 0 20 mm yr on millennial timescales our results exhibit a correlation 2 0 56 between denudation rate and mean catchment elevation in the absence of significant correlation with any other morphometric parameters relief slope catchment size hypsometry etc although such variations in erosion rates have been previously linked to variations in tectonic uplift rate the relatively small size and tectonic homogeneity of our study area exclude a strongly variable tectonic control we interpret the increase in erosion rate with elevation as the effect of frost controlled processes which are strongly temperature dependent we use a one dimensional heat flow model driven by high resolution instrumental temperature records from the study area to correlate the variability in denudation rates with the integral of the absolute temperature gradient within the frost cracking window 3 to 8 c a proxy of the frost cracking intensity for each catchment the results imply that the efficiency of frost cracking constitutes a major control on catchment wide denudation rates in the study area explaining more than half the measured variability in these rates our study shows that present day denudation of the ecrins pelvoux massif is controlled by a climatically driven factor and suggests that frost cracking processes impose an important control on the post glacial topographic evolution of mid latitude mountain belts

el nino forcing on 10be based surface denudation rates in the northwestern peruvian andes abstract high magnitude precipitation events provide large contributions to landscape formation and surface denudation in arid environments here we quantify the precipitation dependent geomorphic processes within the rio piura drainage basin located on the western escarpment of the northern peruvian andes at 5 s latitude in this region monsoonal easterly winds bring precipitation to the 3000 m asl high headwaters from where the annual amount of precipitation decreases downstream toward the pacific coast denudation rates are highest in the knickzones near the headwaters 200 300 mm ky 1 and sediment discharge is limited by the transport capacity of the channel network every few years this situation is perturbed by westerly wind driven heavy precipitation during el nino events and results in supply limited sediment discharge as indicated by bedrock channels the detailed analysis of the stream long profiles of two river basins within the rio piura catchment reveals a distinct knickzone in the transition zone between the easterly and westerly climatic influences suggesting an en nino forcing on the longitudinal channel profiles over at least holocene timescales measured trunk stream catchment wide denudation rates are up to ca 300 mm ky 1 and decrease successively downstream along the river profiles denudation rates of tributary rivers are ca 200 mm ky 1 near the plateau and show a stronger downstream decreasing trend than trunk stream rates this suggests that the landscape is in a transient stage of local relief growth which is driven by fluvial incision this corroborates the results of paleoclimate studies that point towards higher el nino frequencies during the past ca 3000 years leading to higher runoff and more erosion in the trunk channel compared to the hillslopes and thus growth of local relief downstream increases in channel gradient spatially coincide with the reaches of highest precipitation rates during el nino events we therefore interpret that holocene landscape evolution has largely been controlled by climate the ky timescale of the 10 be data together with the transience of the landscape implies that el nino events in northwestern peru have occurred since at least the holocene and that adjustment to channel incision is still taking place

provenance of early palaeozoic sandstones southeastern australia part 1 vertical changes through the bengal fan type deposit abstract ordovician strata of the lachlan fold belt in southeastern australia are dominated by a turbidite succession that in its undeformed state was comparable in size to the modern day bengal fan the ancient fan was derived from the northern part of the cambrian ross delamerian orogenic belt that formed at a convergent boundary between plates containing gondwanaland and part of the palaeo pacific ocean respectively substrate to the submarine fan consisted of mafic volcanic rocks with an immature island arc affinity similar to the eocene izu mariana bonin system sandstone compositions determined from several stratigraphically constrained sections demonstrate a uniform framework composition dominated by monocrystalline quartz with less abundant feldspar polycrystalline quartz metamorphic rock fragments sedimentary rock fragments and mica these indicate derivation from a low grade metamorphic terrain up sequence variation is limited to decreasing feldspar and lithic fragments and increasing quartz indicating increased weathering and lowering of topography in the source terrain over time 25 of counted sandstones in the late ordovician interval contain a small component of mafic intermediate volcanic rock fragments that accompanied a change in palaeocurrent direction from eastwards to northwards in the early silurian the ordovician sequence was disrupted by the formation of several major deformation zones between these zones developed several deep marine sedimentary basins that contain a continuous succession from the ordovician into the early silurian early silurian sandstone is similar in composition to underlying early ordovician rocks except that the feldspar component is generally absent early silurian sandstone was derived from uplifted portions of the ordovician sequence and includes texturally inverted types with sandstone containing a bimodal mixture of coarse well rounded quartz and fine angular quartz

a paleozoic suture in eastern gondwanaland a new tectonic interpretation of southeastern australia tasmania and north victoria land antarctica is given in which a major n s trending lineament representing a suture zone is recognized separating essentially shallow water shelf and continental deposits of latest cambrian or early ordovician age from deeper water ordovician flysch deposits lateral offset of this lineament which is interpreted as a suture along which thrust telescoping and major strike slip faulting occurred could adequately explain the present distribution of major rock types in the three areas and also removes a number of problems previously encountered in correlation

shallow water turbidites an example from the mallacoota beds australia abstract a late ordovician turbidite sequence the mallacoota beds exhibits vertical lithofacies associations that suggest deposition in a fan like environment however there are also features indicating occasional episodic reworking by water currents reworking features include both wave current and unidirectional ripple pavements sharp topped turbidites a difference in current direction between superimposed current rippling and underlying bouma c division ripples lensiodal quartzites and occasional hcs beds comparisons between the mallacoota beds and the depositional products of a variety of open ocean currents would indicate that storm related currents were the most likely reworking mechanism this would indicate that the sequence was deposited within storm wave base depositional depths for part of the sequence are estimated at 90 200 m based on a wave generated ripple model therefore these turbidites may have been produced by storm surge with channeling within the turbidites due to the localisation of rip currents during hurricane conditions a generalised model for the characteristic features of turbidites deposited between fair weather wave base and storm wave base is presented it is suggested that such turbidites will contain only occasional examples of reworking and that the frequency of such reworking events per stratigraphic interval might be used as a relative measure of water depth throughout a sequence moreover those turbidite sequences that have sharp contacts between the sandstones and the overlying mudstones may have been modified by storms and therefore deposited in shallower water than previously thought

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

cosmogenic nuclide derived rates of diffusive and episodic erosion in the glacially sculpted upper rhone valley swiss alps denudation rates of small tributary valleys in the upper rhone valley of the swiss central alps vary by more than an order of magnitude within a very small distance tens of kilometers morphometric data indicate two distinct erosion processes operate in these steep mountain valleys we determined the rates of these processes using cosmogenic beryllium 10 10be in pooled soil and stream sediment samples denudation in deep glacially scoured valleys is characterized by rapid non uniform processes such as debris flows and rock falls in these steep valleys denudation rates are 760 2100 mm kyr 1 in those basins which show minimal previous glacial modification denudation rates are low with 60 560 mm kyr 1 the denudation rate in each basin represents a binary mixture between the rapid non uniform processes and soil creep the soil production rate measured with cosmogenic 10be in soil samples averages at 60 mm kyr 1 mixing calculations suggest that the debris flows and rock falls are occurring at rates up to 3000 7000 mm kyr 1 these very high rates occur in the absence of baselevel lowering since the tributaries drain into the rhone trunk stream up stream of a knickzone the flux weighted spatial average of denudation rates for the upper rhone valley is 1400 mm kyr 1 which is similar to rock uplift rates determined in this area from leveling the pace and location of erosion processes are determined by the oscillation between a glacial and a non glacial state preventing the landscape from reaching equilibrium copyright 2010 john wiley sons ltd

electron spin resonance esr optically stimulated luminescence osl and terrestrial cosmogenic radionuclide tcn dating of quartz from a plio pleistocene sandy formation in the campine area ne belgium abstract the chronostratigraphy of the typical quartz rich white sands that are intensively quarried in the campine area northeastern belgium is poorly constrained in the absence of biostratigraphical data the age of the deposits traditionally assigned to the mol formation is thought to be late pliocene based on sequence stratigraphical correlations ca 2 6 3 6 ma in an attempt to verify this age we used a multi dating method approach on two carefully selected samples in a palaeoseismological trench where the sediment was found to be vertically displaced by the rauw fault three dating methods were used electron spin resonance esr dating optically stimulated luminescence osl dating and cosmogenic radionuclide crn dating in all three cases quartz was found to be a suitable dating material in terms of material properties however the esr dating results based on ti ti li and al centres show strong internal inconsistencies which can be explained by incomplete bleaching as such the youngest esr ages obtained ca 5 ma are regarded as an absolute maximum age in contrast the osl ages of ca 1 5 ma seem to underestimate the sequence stratigraphical age the surface exposure crn dating method using bayesian inversion suggests that a palaeosurface developed around 1 55 0 80 ma and eroded at a rate of ca 15 m ma erosion probably accelerated after ca 0 5 1 ma and posterior to the last major movement along the rauw fault

seafloor zonation in sediment texture on the nova scotian lower continental rise abstract grain size analyses of surface sediment samples from the continental rise below 4000 m off nova scotia clearly show a slope parallel zonation in textural parameters zones of sediment with high sand content 20 are located between 4800 and 4900 m and below 5000 m a zone rich in clay 40 occurs between 4000 and 4800 m the silt clay ratio increases steadily with depth between 4000 and 5100 m these textural trends suggest predominantly slope parallel sedimentary processes on the modern sea floor and conversely little evidence of downslope processes the textural zonations are thought to result from a zonation of bottom currents which are weak at 3500 m but increase regularly to peak speeds greater than 50 cm s 1 on the lower rise at 5000 m the mean position of the northern edge of the gulf stream lies across the southern part of the continental rise over the 4600 to 4900 m depth contours the clay rich band lies upslope from the gulf stream edge beneath a weak to moderate mean abyssal flow toward the southwest in contrast the sand rich zone lies beneath the region of stronger mean southwest flow and beneath the cold filament mapped by weatherly and kelly 1982 this region is also intermittently occupied by the gulf stream and episodic reinforcement of flow in the mean southwest current by bottom sensing eddies from the gulf stream probably creates intermittent high velocity currents that account for the coarse surface texture

excepftonally strong near bottom flows on the continental rise of nova scotia recent current velocity measurements across the lower continental rise of nova scotia show a deep equatorwardflow with speeds maximum 73 centimeters per second among the highest recorded for the deep sea silicate measurements indicate that this flow usually consists of southern source antarctic bottom water these measurements confirm the existence of a second and deeper western boundary flow that was earlier inferredfrom geological observations

global analysis of the stream power law parameters based on worldwide 10be denudation rates abstract the stream power law expressed as e kamsn where e is erosion rate lt 1 k is an erodibility coefficient t 1l 1 2m a is drainage area l 2 s is channel gradient l l and m and n are constants is the most widely used model for bedrock channel incision despite its simplicity and limitations the model has proved useful for topographic evolution knickpoint migration palaeotopography reconstruction and the determination of rock uplift patterns and rates however the unknown parameters k m and n are often fixed arbitrarily or are based on assumptions about the physics of the erosion processes that are not always valid which considerably limits the use and interpretation of the model in this study we compile a unique global data set of published basin averaged erosion rates that use detrital cosmogenic 10be these data n 1457 enable values for fundamental river properties to be empirically constrained often for the first time such as the concavity of the river profile m n ratio or concavity index the link between channel slope and erosion rate slope exponent n and substrate erodibility k these three parameters are calculated for 59 geographic areas using the integral method of channel profile analysis and allow for a global scale analysis in terms of climatic tectonic and environmental settings in order to compare multiple sites we also normalize n and k using a reference concavity index m n 0 5 a multiple regression analysis demonstrates that intuitive or previously demonstrated local scale trends such as the correlation between k and precipitation rates do not appear at a global scale our results suggest that the slope exponent is generally 1 meaning that the relationship between erosion rate and the channel gradient is nonlinear and thus support the hypothesis that incision is a threshold controlled process this result questions the validity of many regional interpretations of climate and or tectonics where the unity of n is routinely assumed

eustatic control of turbidites and winnowed turbidites global changes in sea level primarily the results of tectonism and glaciation control deep sea sedimentation during periods of low sea level the frequency of turbidity currents is greatly increased episodes of low sea level also cause vigorous contour currents which winnow away the fines of turbidites in the rock record the occurrence of most turbidites and winnowed turbidites closely corresponds to global lowstands of paleo sea level this observation may be useful in predicting the occurrence of deep sea reservoir facies in the geologic record

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

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

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

effects of a tectonically triggered wave of incision on riverine exports and soil mineralogy in the luquillo mountains of puerto rico we document the long term response of a tropical mountain stream to tectonics and show how this response exerts a first order spatial control on the delivery of weatherable minerals to forest soils in its catchment these minerals in turn affect nutrient availability and biogeochemical cycles the luquillo mountains is a rainforest covered isolated massif on puerto rico island instead of displaying typical concave up long profiles of most mountain streams the rivers draining the southern flank of these mountains display a systematic downstream increase in gradient using concentrations of in situ produced cosmogenic 10be in quartz from river sediments we find that the downstream steepening is due to the propagation of an erosion wave along the rivers from the coastal plain upstream toward the headwaters decreased 10be concentration along the steepened reaches knickpoint faces or knickzones results from faster denudation of the valley sides around the steepened reaches the upper portions of the steepened reaches knickpoint lips cluster in elevation around the altitude of a flat lying dissected surface traceable around the luquillo mountains inspection of similar platforms over other parts of puerto rico and in the surrounding seas suggests that the dissected surface is an uplifted shore platform formed in the early pliocene 4 my ago upstream of the knickpoints rivers possess alluvial reaches still graded to this uplifted platform they represent relict profiles of the rivers that once drained an island that was surrounded by the now uplifted platform we conclude that the knickpoints initiated when the platform started to rise above the caribbean sea the knickpoints then started propagating upstream defining the front of a slow moving wave of erosion 10be derived catchment scale denudation rates measured above and below the knickpoints indicate a 30 210 increase in denudation associated to the passage of the knickpoints mineralogical analysis of the soils show that soils upstream of the knickpoints overlie deeply depleted saprolite and only contain recalcitrant minerals whereas soils downstream of the knickpoints experience an input of fresh weatherable minerals this influx considerably increases nutrient availability porder et al 2015 in a forest where atmospheric inputs are otherwise the main source of nutrients mcdowell et al 1990 zarin and johnson 1995 pett ridge 2009

tectonic and climatic controls on the spatial distribution of denudation rates in northern chile 18 s to 23 s determined from cosmogenic nuclides in the arid region of northern chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation previous studies of denudation rates from cosmogenic 10be and 26al concentrations are limited to single drainages in this study we examine catchment to orogen scale spatial variation in denudation rates between 18 23 s in the coastal and western cordilleras of northern chile 10be and 26al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment averaged denudation rates at broader scales we examine whether denudation rates and orogen topography reflect the 3d plate geometry of the region cosmogenic nuclide derived denudation rates range from 0 4 0 5 to 20 6 1 5 m myr in the coastal cordillera and from 1 4 0 7 to 168 0 19 8 m myr in the western cordillera the controls on the denudation rates are evaluated using a statistical factor analysis of ten selected catchment parameters denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates drainage area stream order mean elevation mean local relief mean basin slope and analyzed grain size of the sampled sediments moreover denudation rates are better correlated with tectonic controls at catchment scale than orogen scale plate tectonics in the western and coastal cordillera

cosmogenic 10be derived denudation rates of the eastern and southern european alps denudation rates from cosmogenic 10be measured in quartz from recent river sediment have previously been used in the central alps to argue that rock uplift occurs through isostatic response to erosion in the absence of ongoing convergence we present new basin averaged denudation rates from large rivers in the eastern and southern european alps together with a detailed topographic analysis in order to infer the forces driving erosion denudation rates in the eastern and southern alps of 170 1 400 mm ky 1 are within a similar range to those in the central alps for similar lithologies however these denudation rates vary considerably with lithology and their variability generally increases with steeper landscapes where correlations with topographic metrics also become poorer tertiary igneous rocks are associated with steep hillslopes and channels and low denudation rates whereas pre alpine gneisses usually exhibit steep hillslopes and higher denudation rates molasse flysch and schists display lower mean basin slopes and channel gradients and despite their high erodibility low erosion rates exceptionally low denudation rates are also measured in permian rhyolite which has high mean basin slopes we invoke geomorphic inheritance as a major factor controlling erosion such that large erosive glaciers in the late quaternary cold periods were more effective in priming landscapes in the central alps for erosion than in the interior eastern alps however the difference in tectonic evolution of the eastern and central alps potentially adds to differences in their geomorphic response their deep structures differ significantly and unlike the central alps the eastern alps are affected by ongoing tectonic influx due to the slow motion and rotation of adria the result is a complex pattern of high mountain erosion in the eastern alps which has evolved from one confined to the narrow belt of the tauern window in late tertiary time to one affecting the entire underthrust basement orogenic lid and parts of the southern alps today

denudation rates and tectonic geomorphology of the spanish betic cordillera abstract the tectonic control on landscape morphology and long term denudation is largely documented for settings with high uplift rates relatively little is known about the rates of geomorphic response in areas of low tectonic uplift here we evaluate spatial variations in denudation of the spanish betic cordillera based on cosmogenic 10be derived denudation rates denudation rates are compared to published data on rock uplift and exhumation of the betic cordillera to evaluate steady state topography the spatial patterns of catchment wide denudation rates n 20 are then analysed together with topographic metrics of hillslope and channel morphology catchments draining the betic ranges have relatively low denudation rates 64 54 mm kyr 1 but also show large variation as they range from 14 to 246 mm kyr 1 catchment wide denudation is linearly proportional to the mean hillslope gradient and local relief despite large spatial variation in denudation the magnitude and spatial pattern of denudation rates are generally consistent with longer term local uplift rates derived from elevated marine deposits fission track measurements and vertical fault slip rates this might be indicative of a steady state topography where rock uplift is balanced by denudation

sedimentation in the chile trench depositional morphologies lithofacies and stratigraphy the depositional bodies of the chile trench trench fans the axial channel sheeted basins ponded basins and axial sediment lobes control the spatial distribution of modem lithofacies in the basin sheeted basins south of 41 s are presumably fed by closely spaced submarine gullies that approximate a line of source of sediment supply along the base of the slope trench fans 41 s 33 s are built at the mouths of major submarine canyon systems which act as point sources of sediment supply the axial channel follows the northward gravitational gradient draining the distributary networks of trench fans into the longitudinal transport system down gradient northern fan lobes are severely dissected by erosional processes evidently periods of proximal deposition alternate with periods of massive sediment remobilization and progradation of the axial dispersal system into more distal environments channelized basins in the canyon mouth areas yield to sheeted basins depositional surface maintains an axial gradient or ponded basins depositional surface is strictly flat in inter canyon areas tectonic disruption of the oceanic basement can locally augment the axial gradient and stimulate flow channelization or reverse the gradient and induce sediment ponding a large margin parallel sediment lobe is built at the base of a high axial escarpment near 33 s where the axial channel crosses a transverse discontinuity at the convergent plate boundary five lithofacies are defined by q mode factor analysis of sediment textures and hydro dynamic structures in 27 cores from the chile trench the channel facies thick amalgamated sand massive to laminated or cross bedded is deposited by high energy processes within the coarse grained bedload of turbidity currents it forms in distributary and axial channels the levee facies rhythmically bedded internally structureless graded sand and graded silt is deposited from concentrated sediment suspensions that quickly lose momentum during channel spillover it forms on channel flanks although constructional levees are not always present the basin 1 facies more complete bouma sequences both upper and lower flow regime structures forms in ponded basins where flows are confined by a high relief seaward trench wall the basin 2 facies graded and laminated silt lower flow regime structures forms in low energy environments such as interchannel areas distal basins trench walls and elevated topographic features the contourite facies silt and sand laminations winnowed from hemipelagic muds and distal turbidites is best developed in sediment starved basins where geostrophic currents are constricted and accelerated between the steep inner and outer trench walls the trench wedge records a coarsening upward sequence as the oceanic plate migrates toward and into the trench during plate convergence and becomes more proximal to sediment sources along the base of the continental margin near canyon mouths prograding trench fans drive the axial channel seaward into the trench wedge and the coarsening upward sequence is truncated by a time transgressive erosional unconformity abandoned axial channel deposits are carried landward beneath prograding fans to record a fining upward sequence above the basal unconformity channel migration and lobe aggradation may produce fining and coarsening upward sequences on depositional fan lobes but sequences on the erosional lobes are fragmented by numerous truncation surfaces

cosmogenic nuclide based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the swiss alps abstract transient landscape disequilibrium is a common response to climatic fluctuations between glacial and interglacial conditions such landscapes are best suited to the investigation of catchment wide response to changes in incision the geomorphology of the trub and grosse fontanne adjacent stream systems in the napf region of the swiss molasse was analyzed using a 2 m lidar dem the two catchments were impacted by the last glacial maximum lgm even though the glaciers never overrode this region they did however cause base levels to drop by as much as 80 m despite their similar tectonic lithologic and climatic settings these two basins show very different responses to the changing boundary conditions stream profiles in the trub tend to be smooth while in the fontanne numerous knickzones are visible similarly cut and fill terraces are abundant in the trub watershed but absent in the fontanne where deep valleys have been incised the trub appears to be a coupled hillslope channel system because the morphometrics throughout the basin are uniform the morphology of hillslopes upstream of the knickzones in the fontanne is identical to that of the trub basin but different downstream of the knickzones suggesting that the lower reaches of the fontanne have been decoupled from the hillslopes however the rapid incision of the fontanne is having little effect on the adjacent upper hillslopes we tested this interpretation using cosmogenic 10 be derived basin averaged denudation rates and terrace dating the coupled nature of the trub basin is supported by the similarity of denudation rates 350 50 mm ky 1 at a variety of spatial scales upstream of the knickzones rates in the fontanne 380 50 mm ky 1 match those of the trub downstream of the knickzones denudation rates increase to 540 100 mm ky 1 the elevated rates in the downstream areas of the fontanne are due to rapid incision causing a decoupling of the hillslope from the channel basin response time and the magnitude of base level drop exert the principal control over the difference in geomorphic response between the two basins the timing of the filling of the trub valley 17 2 ka and the initial incision of the fontanne 16 3 ka were calculated verifying that these are responses to late glacial perturbations unique lithologic controls allow for one of the fastest regolith production rates yet to be reported 380 mm ky 1

ordovician contourites in the lachlan fold belt eastern australia abstract the ordovician sequence in the northeastern lachlan fold belt consists of three lithologic units representing an overall fining upward succession from turbidites to black shale the lowest unit dominated by turbidite beds represents a small segment of an extensive ordovician submarine fan sequence that covered much of southeastern australia the overlying unit consists predominantly of ripple bedded sandstone with beds 3 5 cm thick these beds are texturally mature containing heavy minerals mica and silt concentrated on the cross laminae the ripple bedded unit has a mean palaeocurrent trend to 321 which is at 60 to sole marks and almost normal to the trend of ripple cross bedding in the underlying and associated turbidite beds this unit is here interpreted as a sandy contourite sequence that can be attributed to contour currents moving northwards along the eastern margin of gondwana from areas of subpolar downwelling off southern africa and america the two major fining upward successions in the ordovician sequence in southeastern australia may reflect eustatic sea level rises during the middle and late ordovician and thus provide evidence of interglacial periods in the darrawilian and late gisbornian to bolindian the contourites would have accumulated in the latter stages of the glacial periods after sea level had risen sufficiently to cut off major sediment supply to the submarine fan but before the temperature had risen to the extent of preventing deep thermohaline circulation

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

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

constraining landscape development of the sri lankan escarpment with cosmogenic nuclides in river sediment escarpments are prominent morphological features along high elevation passive margins recent studies integrating geomorphology thermochronology and cosmogenic nuclide based denudation rate estimates suggest a rapid phase of denudation immediately after the earliest stages of seafloor spreading and subsequent slow denudation rates since to constrain the geomorphic evolution of passive margins we have examined the development of the sri lankan escarpment cosmogenic nuclide data on river sediment along a north south transect across the southern escarpment reveal that the landscape is eroding ten times more rapidly in the escarpment zone 26 to 71 mm kyr 1 than in the high elevation plateau above it and in the lowland plain beneath it 2 6 to 6 2 mm kyr 1 unlike these low denudation rate areas the escarpment denudation is strongly and linearly hill slope dependent this shows that denudation and retreat are tightly interlinked within the escarpment which suggests that the escarpment is evolving by rift parallel retreat rather than by escarpment downwearing supporting evidence is provided by the morphology of rivers draining the escarpment zone these have steep bedrock channels which show sharp and prominent knickpoints along their longitudinal profiles it appears that fluvial processes are driving escarpment retreat as rivers migrate headwards were they incise into the high elevation plateau however the average catchment wide denudation rates of the escarpment zone are low compared to the denudation rates that are estimated for constant escarpment retreat since rifting in common with other escarpments worldwide causes for this slow down can be tectonic change related to flexural bending of the lithosphere climate change that would vary the degree of precipitation focused into the escarpment or the decrease in the contributing catchment area which would reduce the stream power available for fluvial erosion c 2006 elsevier b v all rights reserved

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

calculation of the cosmogenic nuclide production topographic shielding scaling factor for large areas using dems the recent surge of applications using terrestrial cosmogenic nuclides tcns to calculate catchment averaged erosion rates from isotopic concentrations in fluvial sediment and the prospect of coupling tcn production functions with numerical surface process models spms necessitate a fast and accurate algorithm for the calculation of topographic shielding topographic shielding refers to the proportion of the incoming cosmic radiation that is shielded by the surrounding topography the scaling factor being defined as the ratio of the unshielded total minus shielded to the total or maximum cosmic ray flux i e the flux received by a horizontal unobstructed surface topography contributes to the reduction of tcn production by obstructing a certain proportion of the incoming flux and by modifying the angle of incidence available algorithms calculate the proportion of obstructed radiation by dividing the horizon as seen by the sample a grid cell in the case of a dem into arc segments usually of equal length for which the average obstruction heights expressed as zenith angles are calculated the use of these methods is feasible only when dealing with a small number of isolated samples since the identification of obstructions when dealing with an entire area is computationally very intensive this paper describes a method that uses a relief shadow modelling technique to identify those areas of a dem that are under shadow i e shielded and thus to account for the obstructed radiation this method produces results that are very similar to those obtained using a direct implementation of available methods maximum difference between results of c 0 1 the method based on relief shadow modelling is also faster than a direct implementation of any available method and can be readily implemented in any gis system with raster capabilities copyright 2006 john wiley sons ltd

overthrust terranes in the lachlan fold belt southeastern australia the paleozoic history of the lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments four major terranes developed adjacent to the gondwana continental margin and were overthrust in the middle devonian to form a partly composite crust for southeastern australia

stress migration in the north atlantic and intraplate seismicity in scandinavia a proposal abstract recent discussions about the causes of intraplate seismicity in scandinavia suggest that remnant stresses in the lithosphere due to stress accumulation over geological times may have minor impact on the seismicity in fennoscandia an alternative explanation is preferred implying that the driving forces of plate motions are responsible for the intraplate seismicity in scandinavia it is suggested that stresses at the nearest plate margin north atlantic ridge are connected to intraplate stresses scandinavia north america by stress migration diffusion following model of stress continuation in the lithospheric plates thus it may be assumed that seismic energy release along the plate margin is also correlated with intraplate seismicity taking place at intraplate boundaries regional fracture zones or rheological zones of weakness in general