breccia dikes and crater related faults in impact craters on mars erosion and exposure on the floor of a crater 75 km in diameter at the dichotomy boundary environmental conditions on mars are conducive to the modification and erosion of impact craters potentially revealing the nature of their substructure on earth postimpact erosion of complex craters in a wide range of target rocks has revealed the nature and distribution of crater related fault structures and a complex array of breccia and pseudotachylyte dikes which range up to tens of meters in width and tens of kilometers in length we review the characteristics of fault structures breccia dikes and pseudotachylyte dikes on earth showing that they occur in complex network like patterns and are often offset along late stage crater related faults individual faults and dikes can undulate in width and can branch and bifurcate along strike detailed geological analyses of terrestrial craters show that faults and breccia dikes form during each of the major stages of the impact cratering process compression excavation and modification we report here on the discovery of prominent lattice like ridge networks occurring on the floor of a highly modified impact crater 75 km in diameter near the dichotomy boundary of the northern lowland and southern upland interior fill and crater floor units have been exhumed by fluvial and eolian processes to reveal a unit below the crater floor containing a distinctive set of linear ridges of broadly similar width and forming a lattice like pattern ridge exposures range from 1 4 km in length and 65 120 m in width are broadly parallel straight to slightly curving and are cross cut by near orthogonal ridges forming a box or lattice like pattern ridges are exposed on the exhumed crater floor extending from the base of the wall toward the center on the basis of the strong similarities of these features to terrestrial crater related fault structures and breccia dikes we interpret these ridges to be faults and breccia dikes formed below the floor of the crater during the excavation and modification stages of the impact event and subsequently exhumed by erosion the recognition of such features on mars will help in documenting the nature of impact cratering processes and aid in assessment of crustal structure faults and breccia dikes can also be used as data for the assessment of post cratering depths and degrees of landform exhumation

transient sediment supply in a high altitude alpine environment evidenced through a 10be budget of the etages catchment french western alps although beryllium 10 10be concentrations in stream sediments provide useful synoptic views of catchment wide erosion rates little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters here we address this issue by conducting a 10be budget of detrital materials that characterize the morphogenetic domains representative of high altitude environments of the european alps we focus on the etages catchment located in the ecrins pelvoux massif southeast france and illustrate how in situ 10be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream the landscape of the etages catchment is characterized by a geomorphic transient state high topographic gradients and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains beryllium 10 concentrations measured in the etages catchment vary from similar to 1 x 104 to 4 5 x 105 atoms per gram quartz while displaying consistent 10be signatures within each representative morphogenetic unit we show that the basic requirements for inferring catchment wide denudation from 10be concentration measurements are not satisfied in this small dynamic catchment however the distinct 10be signature observed for the geomorphic domains can be used as a tracer we suggest that a terrestrial cosmogenic nuclide tcn budget approach provides a valuable tool for the tracing of material origin in basins where the let nature do the averaging principles may be violated

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

sediment yield exceeds sediment production in arid region drainage basins we use 10 be and 26 al to determine long term sediment generation rates identify significant sediment sources and test for landscape steady state in nahal yael an extensively studied hyperarid drainage basin in southern israel comparing a 33 yr sediment budget with 33 paired 10 be and 26 al analyses indicates that short term sediment yield 113 138 t km 2 yr 1 exceeds long term sediment production 74 16 t km 2 yr 1 by 53 86 the difference suggests that the basin is not in steady state but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield nuclide data indicate that 1 sediment leaving the basin is derived primarily from hillslope colluvium 2 bedrock weathers more rapidly beneath a cover of colluvium than when exposed and 3 long term erosion rates of granite schist and amphibolite are similar

composition morphology and stratigraphy of noachian crust around the isidis basin definitive exposures of pristine ancient crust on mars are rare and the finding that much of the ancient noachian terrain on mars exhibits evidence of phyllosilicate alteration adds further complexity we have analyzed high resolution data from the mars reconnaissance orbiter in the well exposed noachian crust surrounding the isidis basin we focus on data from the compact reconnaissance imaging spectrometer for mars as well as imaging data sets from high resolution imagine science experiment and context imager these data show the lowermost unit of noachian crust in this region is a complex brecciated unit of diverse compositions breccia blocks consisting of unaltered mafic rocks together with rocks showing signatures of fe mg phyllosilicates are commonly observed in regions of good exposure layered or banded phyllosilicate bearing breccia rocks are observed suggestive of pre isidis sedimentary deposits in places the phyllosilicate bearing material appears as a matrix surrounding mafic blocks and the mafic rocks show evidence of complex folded relationships possibly formed in the turbulent flow during emplacement of basin scale ejecta these materials likely include both pre isidis basement rocks as well as the brecciated products of the isidis basin forming event at 3 9 ga a banded olivine unit capped by a mafic unit covers a large topographic and geographic range from northwest of nili fossae to the southern edge of the isidis basin this olivine mafic cap combination superimposes the phyllosilicate bearing basement rocks and distinctly conforms to the underlying basement topography this may be due to draping of the topography by a fluid or tectonic deformation of a previously flatter lying morphology we interpret the draping superposed olivine mafic cap combination to be impact melt from the isidis basin forming event while some distinct post isidis alteration is evident carbonate kaolinite and serpentine the persistence of olivine from the time of isidis basin suggests that large scale aqueous alteration processes had ceased by the time this unit was emplaced

lithologically influenced geomorphic responses to holocene climatic changes in the southern colorado plateau arizona a soil geomorphic and ecologic perspective abstract the semiarid landscape occupied by the navajo and hopi peoples on the colorado plateau in northeastern arizona in the southwestern united states is characterized by an extensive network of deeply incised arroyos since the early 20th century many researchers have proposed that the recent formation of arroyos in this region and also many attributes of modern vegetation communities were caused directly by overgrazing of vegetation by domestic livestock of the navajo other researchers however have proposed other causes for such features such as climatic change we believe that the landforms soils and vegetation of a small area located on antelope mesa in this region underlain by the highly erodible materials of the miocene bidahochi formation may have been more sensitive to minor climatic changes of the holocene than landscapes of massive mesozoic sandstones that dominate the colorado plateau in the antelope mesa area the presence of actively filling channels rather than arroyos in the upper parts of many drainage basins and associated soils and ecologic patterns indicate that the aggradation 1 was initiated in downstream reaches and within the past two centuries 2 may be linked to recently accelerated slope erosion and 3 is unrelated to past or ongoing grazing this suggests the ongoing aggradation may be related to recent minor climatic changes geochronologic and soil geomorphic evidence indicate that the most recent cycle of arroyo incision and filling may be a small scale analogue for larger magnitude older cycles that produced regionally recognizable paired terraces that are attributable to previous holocene climate changes we propose that climatic change and more specifically increases in precipitation caused an acceleration in the erosion of the steep typically minimally vegetated slopes of the bidahochi formation the beginning of the neoglacial period ca 2 3 ka effects of which are documented by other proxy records in this region may be the climatic change that triggered widespread deposition of a large mid holocene alluvial unit in this region alternating episodes of eolian activity and soil formation in the study area and in this general region provide independent evidence of holocene climatic changes our interpretations of the origin of the cut and fill cycles that emphasize the role of drainage basin lithology and differ significantly from previous interpretations emphasize the linkage of climatic changes groundwater levels and arroyo incision this study reveals the importance of integrating soil and ecologic studies with geomorphologic research such an approach may be critical in helping understand how anthropogenically induced climatic changes of the next century could impact geomorphic processes and the ecology of arid and semiarid regions

hydrated silicate minerals on mars observed by the mars reconnaissance orbiter crism instrument phyllosilicates a class of hydrous mineral first definitively identified on mars by the omega observatoire pour la mineralogie l eau les glaces et l activitie instrument preserve a record of the interaction of water with rocks on mars global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy fe mg and al smectite clays this was interpreted to indicate that phyllosilicate formation occurred during the noachian the earliest geological era of mars and that the conditions necessary for phyllosilicate formation moderate to high ph and high water activity were specific to surface environments during the earliest era of mars s history here we report results from the compact reconnaissance imaging spectrometer for mars crism of phyllosilicate rich regions we expand the diversity of phyllosilicate mineralogy with the identification of kaolinite chlorite and illite or muscovite and a new class of hydrated silicate hydrated silica we observe diverse fe mg oh phyllosilicates and find that smectites such as nontronite and saponite are the most common but chlorites are also present in some locations stratigraphic relationships in the nili fossae region show olivine rich materials overlying phyllosilicate bearing units indicating the cessation of aqueous alteration before emplacement of the olivine bearing unit hundreds of detections of fe mg phyllosilicate in rims ejecta and central peaks of craters in the southern highland noachian cratered terrain indicate excavation of altered crust from depth we also find phyllosilicate in sedimentary deposits clearly laid by water these results point to a rich diversity of noachian environments conducive to habitability

the development of polygonal fault systems by syneresis of colloidal sediments abstract polygonal fault systems occur in numerous sedimentary basins worldwide are generally located on passive margins in onlap fill units and tend to comprise the finest grained sediments in this geological setting these fault systems have been most thoroughly described in the central north sea basin and the detailed structure shows a significant correlation with lithological variations both vertically and laterally extension measured in stacked decoupled tiers of polygonal faults correlates positively with both clay fraction and smectite content lateral facies variations are also observed and indicate that time equivalent sequences upslope from the smectite rich polygonally faulted sediments are coarse grained clay poor and undeformed this leads us to believe that the structure and geometry of the fault system are controlled by the colloidal nature of the sediments and that the volumetric contraction measured on seismic sections can be accounted for by syneresis of colloidal smectitic gels during early compaction syneresis results from the spontaneous contraction of a sedimentary gel without evaporation of the constituent pore fluid this process occurs due to the domination of interparticle attractive forces in marine clays dependent on environment and is governed by the change of gel permeability and viscosity with progressive compaction the process of syneresis can account for a number of structural features observed within the fault systems such as tiers of faults the location of maximum fault throw and growth components at upper fault tips as such this paper represents the first attempt to correlate microscale properties of clay rich sediments to their macroscale seismic character

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

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

assessing the mineralogy of the watershed and fan deposits of the jezero crater paleolake system mars we present results from geomorphic mapping and visible to near infrared spectral analyses of the jezero crater paleolake basin and its associated watershed the goal of this study is to understand the provenance of the sedimentary deposits within this open basin lake using a source to sink approach two fan deposits located within the basin have distinct visible to near infrared mineralogic signatures measured by the compact reconnaissance imaging spectrometer for mars crism the northern fan is spectrally characterized by a mixture of mg rich carbonate and olivine while the western fan is characterized by fe mg smectite e g saponite or nontronite with variable amounts of mg rich carbonate and olivine in isolated exposures the watersheds of these deposits contain a variety of geomorphic units that are likely to have supplied sediment to the jezero crater paleolake as the fluvial valleys that fed the basin incise these units the geomorphic units include exposures of fe mg smectite olivine and mg rich carbonate bearing terrain we show that the difference in fan deposit mineralogy is a function of the areal exposure of the major geomorphic units within their watersheds this indicates that the spectrally dominant aqueous alteration minerals in the fan deposits are primarily detrital or transported in nature and did not form in situ we conclude that the aqueous alteration of the units in the watershed occurred prior to the fluvial activity that carved the valleys of the jezero crater paleolake system and that the two periods of aqueous activity are not genetically related

the control of stress history and flaw distribution on the evolution of polygonal fracture networks abstract we use boundary element models of fracture propagation and linkage to investigate the factors controlling the development of two dimensional multi directional polygonal fracture networks characterised by a large number of abutting intersections between fractures the position and orientation of a number of fracture seeds are prescribed in the model which propagate when the applied stress reaches a critical value according to linear elastic fracture mechanics theory the applied boundary condition is a remote isotropic horizontal tension where the stress is increased at a steady rate throughout each model to simulate continued fracture growth realistic polygonal systems are developed with the boundary element model simulations which are comparable with those observed in natural systems such as those found within eocene and oligocene mudrocks in the north sea and on the surface of mars if conditions exist where a small number of fracture seeds propagate and develop significant structures before others then these will dominate the resulting fracture network geometry not only do such early structures represent the largest fractures in the system they also significantly modify the stress field around them preventing some other seeds from developing and influencing the propagation paths of nearby fractures fracture seeding distribution and the rate at which the stress is increased are found to be the most significant parameters affecting the development of fracture network geometry these results suggest that the geometry of evolving fracture networks should be considered not only in terms of the mechanical properties of the deforming material but also in terms of the stress rate driving deformation

10be constrains the sediment sources and sediment yields to the great barrier reef from the tropical barron river catchment queensland australia abstract estimates of long term background sediment generation rates place current and future sediment fluxes to the great barrier reef in context without reliable estimates of sediment generation rates and without identification of the sources of sediment delivered to the reef prior to european settlement c 1850 determining the necessity and effectiveness of contemporary landscape management efforts is difficult here using the 2100 km 2 barron river catchment in queensland australia as a test case we use in situ produced 10 be to derive sediment generation rate estimates and use in situ and meteoric 10 be to identify the source of that sediment which enters the coral sea near cairns previous model based calculations suggested that background sediment yields were up to an order of magnitude lower than contemporary sediment yields in contrast in situ 10 be data indicate that background 43 t km 2 y 1 and contemporary sediment yields 45 t km 2 y 1 for the barron river are similar these data suggest that the reef became established in a sediment flux similar to what it receives today since western agricultural practices increased erosion rates large amounts of sediment mobilized from hillslopes during the last century are probably stored in queensland catchments and will eventually be transported to the coast most likely in flows triggered by rare but powerful tropical cyclones that were more common before european settlement and may increase in strength as climate change warms the south pacific ocean in situ and meteoric 10 be concentrations of coral sea beach sand near cairns are similar to those in rivers on the atherton tablelands suggesting that most sediment is derived from the extensive low gradient uplands rather than the steep more rapidly eroding but beach proximal escarpment

tracking denudation and sediment production and transport with cosmogenic 10be in arid high altitude himalayan half grabens zanskar northern india

ancient igneous intrusions and early expansion of the moon revealed by grail gravity gradiometry the earliest history of the moon is poorly preserved in the surface geologic record due to the high flux of impactors but aspects of that history may be preserved in subsurface structures application of gravity gradiometry to observations by the gravity recovery and interior laboratory grail mission results in the identification of a population of linear gravity anomalies with lengths of hundreds of kilometers inversion of the gravity anomalies indicates elongated positive density anomalies that are interpreted to be ancient vertical tabular intrusions or dikes formed by magmatism in combination with extension of the lithosphere crosscutting relationships support a pre nectarian to nectarian age preceding the end of the heavy bombardment of the moon the distribution orientation and dimensions of the intrusions indicate a globally isotropic extensional stress state arising from an increase in the moon s radius by 0 6 to 4 9 kilometers early in lunar history consistent with predictions of thermal models

steady state reach scale theory for radioactive tracer concentration in a simple channel floodplain system 1 a steady state analytical model is presented for reach scale variation in the concentration of a decaying radioactive tracer associated with sediment particles that regularly pass through an off channel floodplain the floodplain is represented as a series of well mixed sediment reservoirs that continually exchange sediment with the channel the model allows for tributary input and valley wide aggradation or degradation tracer concentration depends on the upstream boundary concentration the tracer and sediment load floodplain geometry and the rates of in floodplain tracer production and or decay the theory predicts relatively modest down channel change in the concentration of long lived isotopes but implies that significant change may occur for 1 tracers with a short enough half life such as 14c or 2 floodplains with sediment residence times that are large enough for cosmogenic production or meteoric fallout to increase tracer concentration in the down valley direction the profiles are shown to be strongly dependent on the grain size distributions of both the sediment load and the floodplain the results imply that down channel 14c profiles have the potential to constrain holocene bed material loads in systems with sufficient storage the theory concisely describes the general importance of a floodplain for modifying in situ produced cosmogenic tracer concentration and can also characterize floodplain importance for fallout radioisotopes i e 10be 210pb or 7be or organic 14c

hydrothermal formation of clay carbonate alteration assemblages in the nili fossae region of mars abstract the compact reconnaissance imaging spectrometer for mars crism has returned observations of the nili fossae region indicating the presence of mg carbonate in small

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

climate and surface properties hydrological response of small arid and semi arid watersheds abstract a positive relationship between annual rainfall and geomorphic processes runoff and erosion rates and environmental factors water regime soil and vegetation cover is often assumed for arid and semi arid areas with an annual rainfall in the range of 100 300 mm this assumption disregards the fact that changes along a climatic gradient at desert margins are not limited to purely climatic factors they are often accompanied by a parallel change in surface properties especially the relative extent of rocky or soil covered surfaces that differ greatly in their response to rainfall this raises the issue whether the change in surface properties along a climatic gradient enhances the assumed positive effects of rainfall increase or limits it the hypothesis advanced in this paper is that runoff generation and rate in arid and semi arid areas are primarily controlled by surface properties rather than by the absolute amounts of storm and annual rain amounts hydrological data collected at two instrumented watersheds located one in an arid rocky area and the second in a semi arid soil covered area support this hypothesis the implications of data obtained for runoff generation and flow continuity under changing climatic conditions are analyzed they point to the fact that the same regional climatic change may have different and even opposite effects on the hydrological response of different adjoining surface units this response is expected to be strongly controlled by the specific local surface conditions that prevailed in the area prior to the climatic change

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

conceptual hydrogeological model of the yonge street aquifer south central ontario a glaciofluvial channel fan setting the yonge street aquifer ysa in the greater toronto area of south central ontario is a prolific municipal supply aquifer it has been considered to be channelized sand and gravel linked to a bedrock valley despite considerable work the fundamental conceptual model for the ysa is not well developed and documented based on high quality data a revised conceptual model of the aquifer is presented seismic profiles define the geometry of the regional stratigraphy with four distinct units bedrock lower sediments newmarket till and oak ridges moraine orm sediment seismic data reveal two generations of roughly north south channels older sub newmarket till channels within lower sediments termed thorncliffe channel and orm related channels termed orm channel that incise both newmarket till and lower sediments the ysa is interpreted to occur within a thorncliffe channel with possible vertical connection to younger orm channels and lateral connection to inter channel lower sediments thorncliffe c

the early martian evolution constraints from basin formation ages impact basin formation ages give insight into the early evolution of a planet the martian basins hellas isidis and argyre provide an important time marker for the cessation of the magnetic dynamo and the crustal thickness distribution both established before 4 ga ago no martian surfaces are older than 4 15 ga based on crater count statistics and all are younger than the oldest lunar ones i show that the heavy bombardment period on the moon and mars evolved similarly but endogenic processes have removed the oldest martian basin record the basin forming projectile population appears to be different from the impactor population observed today in the inner solar system it is yet uncertain whether the heavy bombardment period is cataclysmic or characterized by the decaying flux of planetary formation

timing of surficial process changes down a mojave desert piedmont abstract we measured 10 be and 26 al in 29 sediment samples to infer the history and millennial scale rates of change down a low gradient piedmont a common but enigmatic landform that dominates the mojave desert nuclide data suggest that a large volume of sediment was deposited on the proximal east range road piedmont in fort irwin california 75 500 yr ago since then this material has been stable or eroding slowly in contrast on the distal piedmont 3 5 km from the upland source basins soil stratigraphy suggests that there have been alternating periods of surface stability erosion and deposition over the last 70 000 yr nuclide data from samples amalgamated along cross piedmont transects suggest that long term average down gradient sediment speeds range from 9 cm yr 1 near the uplands to 22 cm yr 1 6 km down piedmont these speeds are similar to 10 be estimated sediment speeds down three other piedmonts in the mojave desert suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates the timing of surface process change down the east range road piedmont is determined by a combination of sediment available in the source basins sediment transport rates and the size of the piedmont

geology of quartz and hydrated silica bearing deposits near antoniadi crater mars 1 the only area on mars where crystalline quartz has been identified from orbit is near antoniadi crater on the northern edge of the syrtis major shield volcano however the method of quartz formation has remained unknown in this study we use high resolution satellite imagery as well as thermal and near infrared spectroscopy to construct a geologic history of these deposits and their local context we find that the quartz bearing deposits are consistently co located with hydrated silica this spatial coherence suggests that the quartz formed as a diagenetic product of amorphous silica rather than as a primary igneous mineral diagenetic quartz is a mature alteration product of hydrated amorphous silica and indicates more persistent water and or higher temperatures at this site beneath the silica bearing rocks we also find spectral evidence for smectites in the lowermost exposed noachian aged breccia a similar stratigraphic sequence smectite bearing breccias beneath deposits containing minerals suggesting a greater degree of alteration has also been found at nearby exposures at nili fossae and toro crater suggesting a widespread sequence of alteration by merging the mineral detections of thermal infrared quartz feldspar and near infrared spectroscopy hydrated silica smectite clays we are able to construct a more complete geologic history from orbit

the formation of irregular polygonal ridge networks nili fossae mars implications for extensive subsurface channelized fluid flow in the noachian abstract roughly 16 000 20 50 m wide morphologically diverse erosionally resistant ridges have been exhumed and mapped in noachian aged terrain across a large region in nili fossae and the nilosyrtis highlands however the formation of these landforms has been widely debated their morphology and geologic context suggest surface processes such as aeolian fluvial and glacial sedimentary deposition are unlikely candidates for their formation possible subsurface ridge formation mechanisms include 1 volcanic dike intrusions along pre existing fractures 2 breccia dikes from impact cratering 3 clastic dikes or deformation bands and 4 chemical alteration or precipitation of minerals in or along pre existing fractures or faults the ridges are being exhumed from a phyllosilicate bearing host rock but whether the ridges themselves have an aqueous origin remains unknown although previous studies used comparative morphology to assess their formation each hypothesized formation mechanism implies different mineralogical suites possibly detectable in remotely sensed spectral data here we combine spectral and morphological analyses to assess the origin of a subset of ridges n 797 that have irregular polygonal ridge network morphology we use observations from the compact reconnaissance imaging spectrometer for mars crism and high resolution imaging science experiment hirise supplemented with context camera ctx imagery to analyze the spectral signatures and geometry in order to 1 measure ridge morphology orientation and intersection angles and 2 isolate the spectral signatures of the ridges from their host unit to evaluate hypothesized ridge formation mechanisms the irregular polygonal nature near orthogonal intersections and lack of dominant orientation are characteristics consistent with fracture propagation under horizontal near isotropic extensional stress in a physically heterogeneous host rock inconsistent with impact or volcanic related features alternatively very shallow clastic intrusion could produce similar ridge geometry our key findings are 1 ridge orientation frequency and distribution suggest mineralization or cementation of subsurface fractures or shallow clastic intrusions as favored formation mechanisms and 2 ridges share all the diagnostic spectral features of mg smectite saponite and or mixed layered talc saponite clays of the host materials however ridges express weaker absorptions if the crism spatial and or spectral resolution has not limited our ability to detect a spectrally unique cementing agent then both grain size or texture and visible to near infrared inactive mineralogy could be responsible for the ridge s weaker spectral absorptions such as quartz and silica some oxide group minerals and amorphous materials our results imply that shallow subsurface groundwater and hydrothermal activity was likely extensive prior to and during the opening of the nili fossae and played an integral role in the formation of the ridges observed throughout the region

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

revised crism spectral parameters and summary products based on the currently detected mineral diversity on mars the investigation of hyperspectral data from the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism and the observatoire pour la mineralogie l eau les glaces et l activitie omega on mars express has revealed an increasingly diverse suite of minerals present on the martian surface a revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in crism targeted observations and designed to capture the known diversity of surface mineralogy on mars is presented here as summary products some of the summary products have strong heritage to omega spectral parameter calculations this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface and successfully highlights and differentiates between locations with differing spectral signatures the revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations

is it possible to quantify pebble abrasion and velocity in rivers using terrestrial cosmogenic nuclides 1 attrition rates and mean transport velocities of coarse fluvial sediments averaged over long periods of time 100 a are yet to be fully quantified a knowledge of long term transport rates would allow us to predict the response of fluvial systems to changes in external conditions while determining clast attrition rates would improve our understanding of fluvial abrasion processes the concentration of terrestrial cosmogenic nuclides tcns in boulders can be modified during river transport by attrition and temporary exposure which are two competing processes in order to evaluate the potential of tcns to quantify these processes a stochastic model of tcn concentration evolution in clasts of different sizes is developed from exhumation on a hillslope to a sampling point in a river the model includes shallow landslides or movement in a regolith and episodic transport of clasts in a sediment layer on the river bed we study the downstream evolution of tcn concentrations for a population of clasts sourced from a localized tcn rich lithology on a hillslope when attrition is strong the model predicts that the variance and maximum of tcn concentrations decrease downstream such a trend is possible only if the dominant hillslope erosion corresponds to shallow landslides natural variability of hillslope processes can hamper the trend a way to limit the scatter is to sample the biggest clasts on the contrary if clast attrition is small and river transport slow tcn concentrations increase downstream in this case combining the tcn concentrations of clasts gathered at several river stations should provide a method to estimate their mean transport rate our results offer guidelines to interpret the downstream evolution of tcn concentration in pebbles and at the surface of boulders

late quaternary history of the chemehuevi mountain piedmont mojave desert deciphered using 10be and 26al we used the cosmogenic nuclides 10 be and 26 al as cosmic ray dosim eters to track sediment movement across the incised chemehuevi mountain piedmont surface the piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the piedmont nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the piedmont from weathering rock analysis of amalgamated sediment samples collected along 4 km long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate piedmont history model results suggest that the chemehuevi mountains are eroding about 40 mm ky 1 whereas the mountain proximal bedrock pediment and the interpiedmont saw tooth range are eroding more slowly 10 to 21 mm ky 1 and 9 5 mm ky 1 respectively cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition at rates between 19 to 39 mm ky 1 and stability over the past 60 ky a change in process from sediment deposition to sediment transport occurred distally on the piedmont approximately 8 ky ago while the mid piedmont piedmont surface has been stable since the mid holocene the incised chemehuevi mountain piedmont is changing at rates similar to planar and uniformly active piedmonts such as those adjacent to the iron and granite mountains all three piedmonts have average sediment grain velocities of decimeters per year long term source basin erosion rates between 35 to 40 mm ky depositional hiatuses around the pleistocene holocene climatic transition from moister to drier conditions and pleistocene deposition rates of 18 to 39 mm ky such similarity in piedmont behavior despite clear differences in morphology and appearance might suggest large scale geologic and climatic controls on the generation transport and deposition of sediment in the mojave desert

cosmogenically enabled sediment budgeting we used 10 be and 26 al to constrain the millennial scale sedi ment and nuclide budget for a common long studied but poorly understood landform in arid regions the desert piedmont we sampled the chemehuevi mountain piedmont a complex multi surfaced landform in the mojave desert western united states the nuclide data indicate that sediment is produced more rapidly 1 1 3 10 5 kg yr 21 km 22 in steep mountain source basins than on the low gradient pediment 4 0 3 10 4 kg yr 21 km 22 or the intra piedmont mountain range 2 5 3 10 4 kg yr 21 km 22 however the bulk of the sediment in transport is derived from erosion of the large abandoned alluvial surface 3 9 3 10 4 kg yr 21 km 22 the combination of mass and nuclide budgeting suggests that sediment transport speeds decrease downslope from tens of meters per year in confined channels on the proximal pediment to decimeters per year in unconfined distributaries on distal wash surfaces the sed iment and nuclide budgeting approach we use is particularly valu able in arid regions where geomorphically significant events are infrequent and dating control is poor thus confounding traditional sediment budgeting techniques

using 10be and 26al to determine sediment generation rates and identify sediment source areas in an arid region drainage basin we measured 10 be and 26 al in 64 sediment and bedrock samples collected throughout the arid 187 km 2 yuma wash drainage basin southwestern arizona from the measurements we determine long term time integrated rates of upland sediment generation 81f 5gm 2 year 1 and bedrock equivalent lowering 30f 2mm a 1 consistent with other estimates for regions of similar climate lithology and topography in a small f 8k m 2 upland sub basin differences in nuclide concentrations between bedrock outcrops and hillslope colluvium suggest weathering of bedrock beneath a colluvial cover is a more significant source of sediment 4010 4 kg year 1 than weathering of exposed bedrock surfaces 1010 4 kg year 1 mixing models constructed from nuclide concentrations of sediment reservoirs identify important sediment source areas hillslope colluvium is the dominant sediment source to the upper reaches of the sub basin channel channel cutting of alluvial terraces is the dominant source in the lower reaches similarities in nuclide concentrations of various sediment reservoirs indicate short sediment storage times 10 3 years nuclide concentrations measured in channel sediment from tributaries of yuma wash and in samples collected along the length of the wash were used to construct mixing models and determine sediment sources to the main stem channel we find an exponential decrease in the channel nuclide concentrations with distance downstream suggesting that as much as 40 of sediment discharged from yuma wash has been recycled from storage within basin fill alluvium sediment generation and denudation rates determined from the main stem are greater 25 than rates determined from upland sub basins suggesting that currently sediment may be exported from the basin more quickly than it is being generated in the uplands independence of nuclide concentration and sediment grain size indicates that channels transport sediment in discrete pulses before rapidly depositing poorly sorted material suggesting that differences in transport times for different size materials are minimal d 2002 elsevier science b v all rights reserved

slow rates of rock surface erosion and sediment production across the namib desert and escarpment southern africa slow erosion has characterized the namib desert the namibian escarpment and the adjacent namibian highlands over the pleistocene paired analyses n 66 of in situ produced 10be and 26al in quartz bearing samples of bedrock primarily from inselbergs of sediment from dry river and stream channels and of clasts from desert surfaces reveal large inventories of these cosmogenic nuclides indicating significant landscape stability over at least the past million years bedrock samples n 47 collected in three transects from the coast across the escarpment and into the highlands show no spatial pattern in elevation normalized nuclide abundance despite a difference in mean annual precipitation map between sample sites at the coast map 400 mm yr 1 average model erosion rates inland of the escarpment 3 2 1 5 n 9 are indistinguishable from average rates seaward of the escarpment 3 6 1 9 n 38 indicating that rock on the pedimented coastal plain is eroding at the same rate as rock in the highlands sediment samples n 3 from small streams suggest that the landscape as a whole is eroding more rapidly than the bedrock outcrops and that a basin in the steep escarpment zone is eroding several times faster 16 m my 1 than either a basin in the highlands 5 m my 1 or a basin in the coastal plain 8 m my 1 data from large rivers n 4 constrain erosion rates averaged over 105 yrs and 104 to 105 km2 between 3 and 9 m my 1 small quartz clasts n 12 collected from four desert surfaces record extraordinarily long variable and in some cases complex exposure histories simple 10be model ages are as high as 1 8 my some minimum total histories considering both 10be and 26al and including both burial and exposure exceed 2 7 my as a group the namibian cosmogenic data do not support the model of significant and on going escarpment retreat the similarity of erosion rates calculated from 10be analysis of fluvial sediments and longer term 107 yr average mass removal rates estimated by others using fission track analysis of rock suggests that namibian erosion rates have reached a steady state and are changing little over time at outcrop scales the concordance of 10be and 26al in most bedrock samples suggests that the model of steady uniform bedrock erosion is valid there is no indication of intermittent burial shedding of thick rock slabs or stripping of previous cover at an intermediate scale a transect of bedrock samples north of gobabeb demonstrates that the northern boundary of the massive namib sand sea has been steady and unshifting similarly low cosmogenically estimated erosion rates across west and central namibia suggest that the landscape is in geomorphic steady state its overall appearance changing only slowly through time

using in situ cosmogenic 10be to identify the source of sediment leaving greenland we use the concentration of in situ 10be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to greenland s sediment budget we sampled along the western eastern and southern margins of the greenland ice sheet and collected sediment sourced from glacerized n 19 and non glacerized terrain n 10 from channels where sediment from glacerized and non glacerized terrain is mixed n 28 from holocene glacial fluvial terraces n 4 and from one sand dune in situ 10be concentrations in sediment range from 1600 to 34 000 atoms g 1 the concentration of in situ 10be in sediment sourced from non glacerized terrain is significantly higher than in sediment sourced from glacerized areas in mixed channel sediment and in terrace sediment that was deposited during the holocene to constrain the timing of landscape exposure for the deglaciated portion of the narsarsuaq field area in southern greenland we measured in situ 10be concentration in bedrock n 5 and boulder n 6 samples paired bedrock and boulder ages are indistinguishable at 1 uncertainty and indicate rapid exposure of the upland slopes at 10 5 ka the isotope concentration in sediment sourced from non glacerized terrain is higher than in sediment sourced from glacerized terrain because the non glacerized landscape has been exposed to cosmic radiation since early holocene deglaciation sediment from glacerized areas contains a low but measurable concentration of 10be that probably accumulated at depth during a prolonged period of exposure probably before the establishment of the greenland ice sheet the concentration of 10be in mixed fluvial sediment and in terrace sediment is low and similar to the concentration in sediment from glacerized areas which indicates that the greenland ice sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled copyright 2014 john wiley sons ltd

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

sensitivity analysis of pediment development through numerical simulation and selected geospatial query abstract dozens of references recognizing pediment landforms in widely varying lithologic climatic and tectonic settings suggest a ubiquity in pediment forming processes on mountain piedmonts worldwide previous modeling work illustrates the development of a unique range in arid semiarid piedmont slope 3 m y 1 restrict pediment development by fostering piedmont incision and or wholesale removal stripping of regolith mantles prior to footslope pediment development simulations illustrate an insensitivity to alternating layers of sandstone and shale 3 15 m thick oriented in various geometric configurations vertical horizontal and dip slope and generating different regolith hydrologic properties and exhibiting weathering rate variations up to 3 fold higher fluxes and residence times of subsurface groundwater in more humid environments as well as dissolution type weathering lead to a thickening of regolith mantles on erosional piedmonts on the order of 10 1 m and an elimination of pediment morphology an initial test of the model sensitivity analysis in arid semiarid environments for which field reconnaissance and detailed geomorphic mapping indicate the presence of pediments controlled by climatic conditions soil hydrologic properties vegetation characteristics and bedrock weathering style that are known and constant supports our modeling results that pediments are more prevalent in hydrologically open basins

from source to sink preserving the cosmogenic 10be derived denudation rate signal of the bolivian andes in sediment of the beni and mamore foreland basins abstract the denudation rate signal of the bolivian andes as measured by cosmogenic 10 be in sediment is preserved in the floodplain of adjacent foreland basins even though these basins store the sediment for thousands of years this conclusion is drawn from comparing published andean source area denudation rates with new cosmogenic 10 be data as measured in the floodplains of the large beni and mamore basins for the entire beni basin including the sediment producing andes and the vast flooded plains of the foreland the cosmogenic nuclide derived denudation rate is 0 45 0 06 mm yr while that of the mamore basin is 0 55 0 19 mm yr by comparison the respective andean source areas erode at averaged rates of 0 37 0 06 mm yr upper beni and at 0 56 0 09 mm yr upper mamore we notice a decrease in variability of denudation rate with increasing spatial scale as small scale processes are averaged out sediment mixing within the floodplain damps scatter of nuclide derived denudation rates picked up in the source area on the temporal scale a remarkable agreement between cosmogenic nuclide derived rates averaging over a few kiloyears with those from fission track dating averaging over millions of years seems to suggest that cosmogenic nuclide derived denudation rates capture the long term erosional characteristics of the mountain belt the sum of these observations suggests that any sample collected along a river traversing a floodplain will yield the denudation rate of the source area this finding opens the unique possibility of constraining cosmogenic nuclide derived paleo sediment budgets for these large basins as the long term spatially averaged denudation rate signal of the sediment producing area is preserved in sedimentary archives

mineralogy and morphology of geologic units at libya montes mars ancient aqueously derived outcrops mafic flows fluvial features and impacts 1 there is ample evidence of both ancient and long lasting fluvial activity and chemical alteration in the libya montes region south of isidis basin the region hosts noachian to amazonian aged surface rocks with extensive outcrops of olivine and pyroxene bearing material libya montes also features surface outcrops and or deposits hosting fe mg smectite fe mg smectite mixed with carbonate and or other fe mg rich phyllosilicates and al smectite these units likely formed through chemical alteration connected with hydrothermal activity resulting from the formation of the isidis basin and or the pervasive fluvial activity throughout this region the morphology and stratigraphy of the aqueous and mafic minerals are described using high resolution imaging science experiment and high resolution stereo camera derived digital terrain models analyses of the compact reconnaissance imaging spectrometer for mars spectra show variations in the chemistry of the fe mg smectite from nontronite like exposures with spectral features near 2 29 and 2 4 m more consistent with fe3 2oh groups in the mineral structure and saponite like outcrops with spectral features near 2 31 and 2 38 m characteristic of mg2 3oh groups these fe mg smectite bearing materials also have bands near 1 9 m due to h2o and near 2 5 m that could be due to the smectite other phyllosilicates and carbonates all regions exhibiting carbonate features near 3 4 3 5 m also have features consistent with the presence of olivine and fe mg smectite indicating that the carbonate signatures occur in rocks likely containing a mixture of these minerals the al smectite bearing rocks have bands near 1 41 1 91 and 2 19 m that are more consistent with beidellite than other al phyllosilicates indicating a higher temperature or diagenetically processed origin for this material our interpretation of the geologic history of this region is that ancient noachian basaltic crustal materials experienced extensive aqueous alteration at the time of the isidis impact during which the montes were also formed followed by emplacement of a rough olivine rich lava or melt and finally the smooth pyroxene bearing caprock unit

erosion rates of the bhutanese himalaya determined using in situ produced 10be abstract western bhutan provides an ideal setting to understand the interplay between uplift erosion and fluvial sediment transport in an active mountain environment using in situ produced 10 be 49 samples and 26 al 5 samples in fluvial sediment from nested catchments throughout the puna tsang chhu drainage basin we examine erosion rates in different geomorphic environments including two high relief regions a glacierized zone in the north and a high rainfall zone in the south as well as remnants of an uplifted lower relief paleosurface between them the erosion rates roughly mirror this north south zonation lower rates avg 388 32 m my 1 n 16 prevail in the low relief zone roughly coinciding with lower relief terrain where mean annual precipitation is 1500 mm yr 1 the highest rates avg 956 160 m my 1 n 13 are in the south 27 10 27 35 n where rainfall is 4000 mm yr 1 high rates avg 700 62 m my 1 n 15 also occur in the northern glacierized region 27 70 28 10 n all 49 purified mineral separates used in this study contain measurable amounts of native 9 be up to 900 g violating the assumption of negligible 9 be that is commonly made in the isotope dilution method used to quantify 10 be to correct for this native 9 be we use high precision replicate measurements of 9 be in each sample to calculate 10 be concentrations from measured isotopic ratios neglecting native 9 be would have led to erosion rate overestimates from 400 the pervasive nature of 9 be in these samples underscores the importance of quantifying the native 9 be concentration in mineral separates used for cosmogenic 10 be analysis

constraints on the crystal chemistry of fe mg rich smectitic clays on mars and links to global alteration trends abstract near infrared remote sensing data of mars have revealed thousands of ancient deposits of fe mg rich smectitic clay minerals within the crust with relevance to past habitability diagnostic metal oh infrared spectroscopic absorptions used to interpret the mineralogy of these phyllosilicates occur at wavelengths of 2 27 2 32 m indicating variable fe mg ratios in the clay structures the objective of this work is to use these near infrared absorptions to constrain the mineralogy of smectites on mars using fe mg rich seafloor clay minerals as mineralogical and spectroscopic analogs for martian clay minerals we show how crystal chemical substitution and mixed layering affect the position of the diagnostic metal oh spectral feature in smectitic clay minerals crystal chemistry of smectites detected on mars were quantitatively constrained with infrared data and categorized into four mineralogical groups possible alteration processes are constrained by comparisons of clay chemistry detected by remote sensing techniques to the chemistry of candidate protoliths of the four groups identified three of them indicate significant segregation of fe from mg suggestive of alteration under water rich and or oxidizing conditions on mars the fourth group with low fe mg ratios may result from alteration in reducing or water limited conditions potentially in subsurface environments some samples are interstratified di trioctahedral clay minerals that have characteristics of dioctahedral clay minerals but clear chemical evidence for trioctahedral sheets approximately 70 of smectite deposits previously detected on mars are classified as fe rich feo mgo 10 only 22 of detections are trioctahedral and relatively mg rich an additional 8 are difficult to characterize but might be very fe rich the segregation of fe from mg in martian clay minerals suggests that mg should be enriched in other contemporaneous deposits such as chlorides and carbonates

extensive linear ridge networks in nili fossae and nilosyrtis mars implications for fluid flow in the ancient crust 1 we have undertaken high resolution mapping of the distribution physical characteristics orientation and stratigraphic occurrence of 4000 linear ridge segments in two study areas the nilosyrtis highlands and the nili fossae region covering 1 105 km2 ridges are typically hundreds of meters in length meters in width and up to tens of meters in height ridges form intersecting networks of anastomosing and bifurcating segments and consequently have variable orientations ridges are expressed in altered and brecciated basement materials on the floors and rims of impact craters deeply eroded by fluvial and other processes the ridge bearing basement is the lowest exposed stratigraphic unit and is overlain by a relatively unaltered mafic cap rock ridges are observed to terminate at the contact of these two units we interpret the ridges to represent a complex of fractures faults shear zones clastic and melt bearing dikes and pseudotachylytes that have been variably indurated by fluid percolation and mineralization the fluid conduits were hardened relative to the host rock and are expressed as ridges due to differential erosion the orientations of the exhumed ridges record the state of stress in the crust at the time of formation in nili fossae a significant population of ridges is aligned with the orientations of the nili fossae graben indicating that their emplacement may be related to crustal loading of the isidis basin after the impact event the association of ridges with the hydrated mineral bearing basement suggests that in the postimpact environment the fractures served as conduits of preferential fluid flow which were cemented by mineral precipitation

stochastic model for the long term transport of stored sediment in a river channel we develop a stochastic model for the transport of stored sediment down a river channel the model is based on probabilities of transition of particles among four different sediment storage reservoirs called active often mobilized semiactive inactive and stable hardly ever mobilized the probabilities are derived from computed sediment residence times two aspects of sediment storage are investigated flushing times of sediment out of a storage reservoir and changes in the quantity of sediment stored in different reservoirs due to seasonal sediment transport into and out of a reach we apply the model to redwood creek a gravel bed river in northern california although the redwood creek data set is incomplete the application serves as an example of the sorts of analyses that can be done with the method the application also provides insights into the sediment storage process sediment flushing times are highly dependent on the degree of interaction of the stable reservoir with the more mobile sediment reservoirs the most infrequent and highest intensity storm events which mobilize the stable reservoir are responsible for the long term shifts in sediment storage turnover times of channel sediment in all but the stable reservoir are on the order of 750 years suggesting this is all the time needed for thorough interchange between these sediment compartments and cycling of most sediment particles from the initial reservoir to the ocean finally the markov model has adequately characterized sediment storage changes in redwood creek for 1947 1982 especially for the active reservoir the model replicates field observation of the passage of a slug of sediment through the active reservoir of the middle reach of redwood creek in the 18 years following a major storm in 1964 that introduced large quantities of landslide debris to the channel

use of cosmogenic radionuclides as a sediment tracer in the santa cruz littoral cell california united states we demonstrate that cosmogenic radionuclides can be employed to trace sediment when the sources have sufficiently distinct concentrations and develop a theoretical mixing model for a rocky coastline littoral system we combine the resulting mixing model with existing cosmogenic radionuclide methods that quantify river inputs and terrace ages to determine the major components of the long term littoral sediment budget of the santa cruz california coastline sediment derived from coastal basins eroding at 0 2 mm yr has a much lower concentration than sediment derived from 60 84 ka terrace sands atop backwearing seacliffs the complex pattern of cosmogenic radionuclide concentrations in littoral sands along 100 km of coastline can be explained by mixing sediment derived from seacliffs backwearing at 10 cm yr with that delivered by rivers having widely different amounts of sediment discharge

impact of glacial erosion on 10 be concentrations in fluvial sediments of the marsyandi catchment central nepal several processes contribute to denudation in high mountain environments of these glacial erosion is particularly difficult to constrain despite its critical importance in the evolution of many mountain ranges in this study we present a new data set of 10be concentrations in fluvial sediments sampled along the marsyandi river and its main tributaries in central nepal we interpret the 10be concentrations as being significantly impacted by glacially derived sediments along the marsyandi river such additions complicate conventional interpretations of 10be derived catchment scale denudation rates using a simple linear mass conservation formulation we invert our data set in order to separate the different denudational contributions to the observed signal as well as to constrain their magnitude and spatial distribution our results suggest significant variations in glacial erosion both in space and magnitude within the marsyandi catchment

control of impact crater fracture systems on subsurface hydrology ground subsidence and collapse mars 1 noachian layered materials are pervasively exposed throughout the highlands of mars the layered deposits in places many kilometers thick exhibit impact craters of diverse morphologic characteristics ranging from highly degraded to pristine most of which formed during the period of heavy bombardment in addition exhumed impact craters ancient channels and fluvial and alluvial fans are visible in the layered deposits through moc imagery these features are more abundant in noachian terrains which indicates relatively high erosion rates during ancient mars that competed with heavy meteoritic bombardment the noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation here we propose that impact craters buried and exposed and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic driven hydrothermal activity in and surrounding the tharsis region for example the formation of chaotic terrains the source regions of the circum chryse outflow channel system and a large diversity of collapse structures including impact crater moats and pit chains appear to be the result of enhanced hydrothermal activity

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

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

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

spatial and temporal replicability of meteoric and in situ 10be concentrations in fluvial sediment cosmogenic isotopes short lived radionuclides elemental concentrations and thermochronometeric indicators are measured in river sand to quantify erosion rates trace sediment sources and or infer erosional processes interpretations of detrital sediment analyses are often based on the rarely tested assumption of time invariant tracer concentration better understanding of when and where this assumption breaks down and what sampling strategies minimize temporal and small scale spatial variance will improve science done using detrital river sediment here we present new and previously published spatial and temporal replicates measured for in situ and meteoric 10be 10bei and 10bem our new data include 113 replicate pairs taken from agricultural and or tectonically active watersheds in china months to millennia apart and spatial replicates taken up to 2 km apart on the same day the mean percent difference is 10 122 to 150 for both systems considered together the mode is close to 0 for both systems and 36 of pairs of samples replicate within our analytical accuracy at 2 we find that 10bei replicates better than 10bem p 0 01 10bei replicability is worse in steeper basins suggesting that stochastic processes i e landslides affect reproducibility 10bem replicability is worse in larger basins suggesting non conservative behavior of 10bem as sediment moves downstream our results are consistent with the few previously published replicate studies considering all replicate data in a wide range of landscapes in areas with deep erosional processes replicability is poor in other areas replicability is good this suggests that in steep tectonically active and or agricultural landscapes individual detrital sediment measurements do not represent upstream rates as well as larger populations of samples to ensure that measurements are representative of the upstream watershed our data suggest that samples be amalgamated either over time or from several places close by in the same channel

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

major episodes of geologic history of isidis planitia on mars abstract we have mapped the area of isidis planitia 1 27 n 75 103 e in order to assess the geologic history of this region using modern data sets such as mola topography and the high resolution images provided by the hrsc ctx and hirise cameras results of our mapping show that the geologic history of isidis planitia consists of three principal episodes 1 impact dominated episode noachian until 3 8 ga during this time the oldest materials in the study area were formed mostly by impact reworking and mass wasting other processes e g volcanism and fluvial glacial activity likely operated at this time but played a subordinate role 2 an episode related to volcanic and fluvial glacial activities late noachian early amazonian 3 8 2 8 ga volcanism appears as the most important process at the beginning of this episode 3 8 3 5 ga and was responsible for the formation of a large circum isidis volcanic province by the early hesperian epoch volcanic materials covered large portions of the isidis rim almost completely buried the previous crater record on the floor of the isidis basin and probably were the major contributors to the filling of the basin fluvial glacial processes prevailed closer to the end of the episode early hesperian early amazonian 3 5 2 8 ga and were responsible for widespread resurfacing in the isidis planitia region mostly at 3 1 3 4 ga glaciers and or ice sheets probably resulted in a massive glaciation of the rim and the floor of the isidis basin the total volume of material eroded from the isidis rim by glacial and fluvial activity is estimated to be about 35 000 50 000 km 3 which is equivalent to a composite layer about 40 60 m thick on entire floor of the basin more important however is that the eroded materials were likely saturated with ice water and could form wet deposits on the floor 3 wind dominated episode since early amazonian 2 8 ga wind activity dominated the later geologic history of isidis planitia but resulted only in minor modification of the surface

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

consistent slow exhumation in a late cenozoic glaciated landscape the presidential and carter ranges of the white mountains in new hampshire usa abstract to investigate the ability of the onset of quaternary glaciations to drive an acceleration in erosion rates we compare short timescale 103 104 yr erosion rates using the in situ terrestrial cosmogenic nuclide tcn 10be to longer time scale exhumation rates 106 107 yr using the apatite u th he method in the presidential and carter ranges of the white mountains in new hampshire usa our results are generally consistent with but refine previous studies using similar techniques resulting u th he ages and thermal modeling from mt washington in the presidential range n 4 91 7 to 117 3 ma suggest that exhumation rates from the late cretaceous to the present were slow

tectonic implications of fluvial incision and pediment deformation at the northern margin of the central anatolian plateau based on multiple cosmogenic nuclides 1 we document quaternary fluvial incision driven by fault controlled surface deformation in the inverted intermontane gok rmak basin in the central pontide mountains along the northern margin of the central anatolian plateau in situ produced 10be 21ne and 36cl concentrations from gravel covered fluvial terraces and pediment surfaces along the trunk stream of the basin the gok rmak river yield model exposure ages ranging from 7 1 ka to 346 45 ka and average fluvial incision rates over the past 350 ka of 0 28 0 01 mm a 1 similarities between river incision rates and coastal uplift rates at the black sea coast suggest that regional uplift is responsible for the river incision model exposure ages of deformed pediment surfaces along tributaries of the trunk stream range from 60 5 ka to 110 10 ka demonstrating that the thrust faults responsible for pediment deformation were active after those times and were likely active earlier as well as explaining the topographic relief of the region together our data demonstrate cumulative incision that is linked to active internal shortening and uplift of 0 3 mm a 1 in the central pontide orogenic wedge which may ultimately contribute to the lateral growth of the northern anatolian plateau

implications for early hydrothermal environments on mars through the spectral evidence for carbonation and chloritization reactions in the nili fossae region 1 previous identification of serpentine and magnesium carbonate in the eastern nili fossae region of mars indicates hydrothermal alteration of an olivine rich protolith here we characterize fe mg phyllosilicates associated with these units and present spectral evidence for the presence of a talc component distinguishable from saponite locations with magnesium carbonate are exclusively associated with talc related phyllosilicates in the westernmost portions of the nili fossae region where a mafic protolith dominates fe mg phyllosilicates display spectral evidence for a wide degree of chloritization we propose that noachian fe mg smectites were uniformly buried by hesperian lava flows that initiated hydrothermal alteration in the eastern nili fossae region the chloritization of smectites may have produced silica rich fluids necessary for the serpentinization of olivine temperature and depth constraints indicated by their distribution also suggest a hydrothermal system was present the subsequent carbonation of serpentine and or olivine in eastern nili fossae while requiring an additional co2 source provides an explanation for the limited occurrence of serpentine and the colocation of carbonate and talc bearing material throughout this area the consequence of the hypothesized carbonation reaction and the presence of serpentine provides geochemical constraints for the proportion of co2 present in the fluids that interacted with the protolith if this carbonation reaction was a widespread phenomenon it may have been an important process in the ancient martian carbon cycle and could have provided a sink for co2 in the past

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

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

isotopic insights into smoothening of abandoned fan surfaces southern california cosmogenic nuclide concentrations measured on abandoned fan surfaces along the mojave section of the san andreas fault suggest that sediment is generated transported and removed from the fans on the order of 30 40 kyr we measured in situ produced cosmogenic 10 be and in some cases 26 al in boulders n 15 surface sediment n 15 and one depth profile n 9 nuclide concentrations in surface sediments and boulders underestimate fan ages suggesting that 10 be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages field observations grain size distribution and cosmogenic nuclide data suggest that over time boulders weather into grus and the bar sediments diffuse into the adjacent swales as fans grow older the relief between bars and swales decreases the sediment transport rate from bars to swales decreases and the surface processes that erode the fan become uniform over the entire fan surface the nuclide data therefore suggest that over time the difference in 10 be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized resulting in a common surface lowering rate and common 10 be concentrations across the fan during this phase the entire fan is lowered homogeneously at a rate of 10 15 mm kyr 1

tracking paraglacial sediment with cosmogenic 10 be using an example from the northwest scottish highlands abstract beryllium 10 concentrations in samples of sediment and bedrock from five study sites across the scottish highlands trace paraglacial sediment sources and define the nature of glacial erosion for the late quaternary exposure ages derived from 10 be concentrations in ridge and lower elevation bedrock range from 10 to 33 ka which suggest that polythermal ice and warm based ice were primarily responsible for producing glacial sediment comparisons of 10 be concentrations between catchment wide sediment 2 06 0 34 10 4 to 11 24 1 54 10 4 atoms g 1 sio 2 n 33 near surface deposits 2 71 0 33 10 4 to 3 48 0 49 10 4 atoms g 1 sio 2 n 6 4 m thick deep till 0 68 10 4 10 be atoms g 1 sio 2 n 1 ridge bedrock 8 93 0 47 10 4 to 34 05 1 66 10 4 atoms g 1 sio 2 n 20 and lower elevation polished bedrock 6 74 0 67 10 4 to 12 65 0 7 10 4 atoms g 1 sio 2 n 5 indicate that most sand fluxing through catchments in the scottish highlands is sourced from the remobilization and vertical mixing of near surface deposits these findings indicate that glaciogenic material continues to dominate paraglacial sediment budgets more than 11 ka after deglaciation

cosmogenic exposure and erosion history of australian bedrock landforms exceptionally high activities of in situ produced 1 0 be and 2 6 al indicate that australian bedrock surfaces are some of the most stable in the world these cosmogenic nuclides demonstrate that australian granite exposed and sampled at 10 sites along a transect from the eyre peninsula 33 s to the kakadu area in the northern territory 14 s has in some places eroded only decimeters over the past million years however nuclide activities are not saturated in any of the 61 exposed samples we analyzed mandating that the surfaces we sampled are losing mass albeit slowly over time such mass loss indicates that inselbergs are dynamic landforms confounding the assignment of discreet ages to inselberg surfaces nevertheless the differential between slow rates of erosion measured on the very stable uppermost parts of these landforms and the more rapid rates measured below their flanks and below the adjacent grus covered planes suggests that the forms of many large inselbergs which stand meters to tens of meters high must be at least tertiary in age and possibly much older activities of 1 0 be and 2 6 al in 61 exposed australian samples range from 5 1 0 1 10 6 to 5 3 0 6 x 10 5 atoms g 1 and 2 1 0 1 x 10 7 to 3 4 0 5 x 10 6 atoms g 1 respectively normalized to sea level at latitudes of 60 using only neutron scaling activities of 1 0 be and 2 6 al in seven shielded samples 3 5 13 m below the surface are much lower ranging from 3 4 0 2 x 10 4 to 7 0 0 1 x 10 4 atoms g 1 and 1 6 0 1 x 10 5 to 2 8 0 2 x 10 5 atoms g 1 respectively 2 6 al 1 0 be ratios of exposed samples range from 3 89 0 19 to 6 29 0 82 if 2 uncertainty ranges and a nominal sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 are considered ratio data for all but one surface sample are consistent with continuous surface or near surface exposure and or erosion rock surfaces farther north in australia where the climate is more humid have lower nuclide activities thus we infer that surface stability is inversely related to mean annual precipitation from 61 exposed samples we calculated maximum limiting single nuclide model erosion rates of 0 3 0 1 to 5 7 1 0 m m y and minimum limiting single nuclide model exposure ages of 105 16 to 1310 190 ka by assuming a sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 seven shielded samples in which the nuclide inventory is muon generated also have nuclide activities consistent with similarly low rates of erosion but over even longer time scales it appears that the eyre peninsula inselbergs have been and are eroding so slowly that they may well be direct descendents of cenozoic and perhaps even mesozoic forms

rates of sediment supply to arroyos from upland erosion determined using in situ produced cosmogenic 10be and 26al using 10be and 26al measured in sediment and bedrock we quantify rates of upland erosion and sediment supply to a small basin in northwestern new mexico this and many other similar basins in the southwestern united states have been affected by cycles of arroyo incision and backfilling several times in the past few millennia the sediment generation 275 65 g m 2 yr 1 and bedrock equivalent lowering rates 102 24 m myr 1 we determine are sufficient to support at least three arroyo cycles in the past 3 000 years consistent with rates calculated from a physical sediment budget within the basin and regional rates determined using other techniques nuclide concentrations measured in different sediment sources and reservoirs suggest that the arroyo is a good spatial and temporal integrator of sediment and associated nuclide concentrations from throughout the basin that the basin is in steady state and that nuclide concentration is independent of sediment grain size differences between nuclide concentrations measured in sediment sources and reservoirs reflect sediment residence times and indicate that subcolluvial bedrock weathering on hillslopes supplies more sediment to the basin than erosion of exposed bedrock

retreating ice research in pro glacial areas matters glacier forefields are landscapes in transition from glacial to non glacial conditions this implies intense geomorphic hydrological and ecological dynamics with important on and off site effects this special issue collects 13 papers covering recent research in both sub polar and alpine proglacial environments that focus on i proglacial sediment sources ii proglacial rivers iii proglacial lakes iv ground water and ice and v the development of soil and vegetation in its interplay with morphodynamics advances in mapping surveying and geophysical techniques form the basis for research perspectives related to the historical evolution of proglacial areas the understanding of complex interactions of multiple processes and the effects of continued glacier recession

an in situ record of major environmental transitions on early mars at northeast syrtis major the noachian hesperian transition on mars was a period marked by changes in volcanic processes and styles of aqueous alteration understanding the timing and nature of environmental change requires the exploration of units recording both sets of processes herein we report the compositional stratigraphy of distinctive noachian to hesperian units along the northeastern margin of the syrtis major volcanic flows a layered polyhydrated sulfate bearing unit with jarosite ridges has been discovered beneath the syrtis major lava flows and above the regionally extensive stratigraphy of noachian plains units reported previously sequential clay carbonate and sulfate bearing units formed in situ and record a transition from alkaline ph to acidic ph waters the sequence is chronologically bookended by the isidis impact and syrtis major flows and is one of the most temporally constrained and well preserved stratigraphic sections from early mars available for landed exploration

tracking painted pebbles short term rates of sediment movement on four mojave desert piedmont surfaces 1 to quantify short term sediment movement rates across mojave desert piedmonts 1600 painted and numbered pebbles were laid out in paired orthogonal 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later pebble lines cross shallow 5 15 cm ephemeral channels and adjacent unconsolidated interfluves the latter being the dominant landform at all sites two sites are located on surfaces that have been or are impacted by military training activities including the use of tracked vehicles the two other sites have not been disturbed by human impact three different processes transport pebbles episodic streamflow in ephemeral channels transports a few pebbles long distances decimeters to meters down gradient bioturbation moves many pebbles small distances centimeters in any direction and vehicular disturbance transports pebbles varying distances centimeters to meters in any direction significant down gradient sediment movement occurred dominantly in channels where flowing water was concentrated interfluves were stable surfaces where little transport occurred off road vehicle use is coincident with accelerated pebble movement pebbles moved further and faster down gradient at the disturbed iron mountain and east range road sites mean speeds of 0 18 and 0 34 m yr 1 respectively than at the undisturbed chemehuevi and goldstone sites mean speeds of 0 17 and 0 02 m yr 1 respectively mean pebble movement is highly and negatively correlated with vegetation density short term pebble movement rates are several times lower than long term 103 to 104 year rates suggesting the importance of rare extreme precipitation events for sediment transport such as those of fall and winter 2004