testing the sensitivity of geomorphic indices in areas of low rate active folding eastern betic cordillera spain abstract active deformation structures have an incidence in topography that can be quantified by using geomorphic indices most of these indices have been checked in faulted regions with high deformation rates the application of several geomorphic indices hypsometric curve analysis normalized stream length gradient and valley width to valley height ratio to the drainage network of the southern limb of the sierra de las estancias antiform internal zones eastern betic cordillera where low rate active folding has been recognized allows us to investigate the suitability of these indices to identify active structures in such a scenario hypsometric curves clearly identify regions with recent uplift and young topography but they do not provide any constraint on the location of active folds local valley width to valley height index variations have been detected just coinciding whit the position of ene wsw active folds normalized stream length gradient index serves to locate active folds in areas of hard rock substratum but not in those areas with soft sediments neogene quaternary sedimentary basins this is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors in view of these results we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low rate uplift related to active folding with the best results obtained in hard rock areas

some considerations concerning seismic geomorphology and paleoseismology abstract seismic geomorphology studies landforms which developed in connection with earthquakes among them two different end members may be distinguished 1 seismo tectonic landforms including surface faults and fractures land uplift and subsidence at different scales surface bulges elongate ridges and any other permanent ground deformations directly related to tectonic stress and 2 seismo gravitational landforms such as landslides deep seated gravitational slope deformations sinkholes and fissures due to sediment compaction or liquefaction and sand blows connected with both seismic shaking and gravitational stress a clear cut distinction between the two categories of landforms is not always easy to make and in many instances not really useful while there are in many cases ground effects that might be and should be considered as simultaneous combinations of seismo tectonic and seismo gravitational processes this applies especially to surface fracturing and faulting which could be the combined result of tectonic stress stress produced by seismic shaking and gravitational stress the objective of this paper is to review selected case histories mainly from italy and the mediterranean region in order to show the importance of a comprehensive study of earthquake generated landforms for understanding the seismicity level of the area under investigation we argue that in earthquake prone areas seismic landforms often constitute typical patterns seismic landscapes whose recognition mapping and paleoseismological analysis may help in the evaluation of seismic hazards

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

soil profiles as indicators of mineral weathering rates and organic interactions for a pennsylvania diabase abstract basaltic bedrock dissolves quickly and its weathering rate is therefore important towards controlling the composition of natural waters soil formation and co 2 concentrations in the atmosphere despite its importance however few reports of basalt or diabase and gabbro weathering rates exist in the literature and most have been measured in laboratory dissolution experiments or based on watershed studies here using elemental profiles measured through regolith on a jurassic diabase dike in south central pennsylvania we calculate time integrated log dissolution rates mol m 2 s 1 of the primary minerals plagioclase 14 9 s 1 and augite 14 8 and of smectite 17 6 a secondary clay mineral formed in the soil characteristic patterns in elemental profiles are consistent with preserved signatures of corestone formation elemental and mineral signatures of the soils relative to the parent rock are compared to predictions from citrate containing basalt column dissolution experiments depletion of apatite and of al fe mn ti p y ni cr sc v ga cu zn and la are observed in the upper meter of the profile relative to the parent rock

rates of weathering rind formation on costa rican basalt weathering rind thicknesses were measured on 200 basaltic clasts collected from three regionally extensive alluvial fill terraces qt 1 qt 2 and qt 3 preserved along the pacific coast of costa rica mass balance calculations suggest that conversion of unweathered basaltic core minerals plagioclase and augite to authigenic minerals in the porous rind kaolinite allophane gibbsite fe oxyhydroxides is iso volumetric and ti and zr are relatively immobile the hierarchy of cation mobility ca na k mg si al fe p is similar to other tropical weathering profiles and is indicative of differential rates of mineral weathering anorthite albite hypersthene orthoclase apatite alteration profiles across the cm thick rinds document dissolution of plagioclase and augite and the growth of kaolinite with subsequent dissolution of kaolinite and precipitation of gibbsite as weathering rinds age the rate of weathering rind advance is evaluated using a diffusion limited model which predicts a parabolic rate law for weathering rind thickness rr as a function of time t rr t and an interface limited model which predicts a linear rate law for weathering rind thickness as a function of time rr kappt in these rate laws is a diffusion parameter and kapp is an apparent rate constant the rate of advance is best fit by the interface model terrace exposures are confined to the lower reaches of streams draining the pacific slope near the coast where the stream gradient is less than 3 m km and terrace deposition is influenced by eustatic sea level fluctuations geomorphological evidence is consistent with terrace deposition coincident with sea level maxima when the stream gradient would be lowest assigning the most weathered regionally extensive terrace qt 1 mean rind thickness 6 9 0 6cm to oxygen isotope stage ois 7 ca 240 ka and assuming that at time 0 rind thickness 0 it is inferred that terrace qt 2 rr 2 9 0 1 cm is coincident with stage 5e ca 125 ka and that qt 3 rr 0 9 0 1 cm is consistent with ois 3 ca 37 ka these assignments yield a value of kapp of 8 6 10 13 cm s 1 r 2 0 99 only this value satisfies both the existing age controls and yields ages coincident with sea level maxima using this value elemental weathering release fluxes across a weathering rind from qt 2 range from 6 0 10 9 mol si m 2 s 1 to 2 5 10 11 mol km 2 s 1 the rate of rind advance for the costa rican terraces is 2 8 10 7 my r 1 basalt rind formation rates in lower temperature settings described in the literature are also consistent with interface controlled weathering with an apparent activation energy of about 50 kj mol 1 rates of rind formation in costa rica are an order of magnitude slower than reported for global averages of soil formation rates copyright 2004 elsevier ltd

the declining but non rejuvenating base level the lisan lake the dead sea area israel laboratory experiments investigating the effects of a lowering base level do not simulate natural eustatic lowering along concave river profiles the field data on this issue are also quite limited in evaluating the control exercised by lowering base level on a drainage network distinction must be made between its influence and those of other hydromorphological processes operating within the basin field data on morphological relations based on photogrammetric mapping and longitudinal profiling have been gathered in the dead sea area israel where a rapid fall in base level has occurred during the holocene the study area is an entrenched fan delta with a sequence of 14 unpaired fan terraces which die out at intersection points within an alluvial fan system the results suggest that the intersection points did not function as base levels the receding base level played only a passive role allowing entrenchment without transmitting a head cutting feedback basinwards the arid environment caused a delay in transmission of information through the system the results support the model of short episodic and discontinuous erosional events inherent in the evolution of drainage basins it is suggested that base level effects in temperate and humid regions are not transferrable to arid zones

controls on fan development evidence from fan morphometry and sedimentology sierra nevada se spain abstract we have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the late pleistocene as a result of the recent uplift of the sierra nevada betic cordillera spain three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans in connection with a decrease in the volume of fines available in the source areas the larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment with the appearance of less elongated fans in the rest of the system where subsidence is less more elongated fans appear with the development of incised channels and irregular distribution of sediment in depositional lobes this involves the appearance of markedly asymmetric transverse profiles as well as lengthy recurrence between the sedimentation events on particular sectors of the fans where headward eroding gullies develop the lithology of the source area where intensely fractured rocks are found is responsible for an important sediment supply and a significant degree of clast sorting from the source area consequently a weak longitudinal trend in particle size can be recognised which influences the predominance of longitudinal constant slope profiles and anomalous relations between both fan area and fan slope and their drainage areas recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments where mass flows are trapped and the fans present a subsequently higher proportion of sheet flows recent piracy phenomena can be recognised in some of the drainage basins which indicate rejuvenation of the source area in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile due to the recent nature of the processes the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

holocene microweathering rates and processes on ice eroded bedrock roldal area hardangervidda southern norway post glacial weathering of ice eroded metamorphic bedrock was investigated in the roldal area 60 n of the hardangervidda plateau in southern norway quartz veins were used as reference surfaces to determine a mean post glacial surface lowering rate of 0 55 mm ka 1 chemical characteristics of late season runoff were determined for one catchment snoskar and a chemical erosion rate of 4 9 t km 2 a 1 was obtained a mean in situ fracture enlargement due to microweathering of 0 12 mm ka 1 was also determined these rates are low although comparable with similar environments in cold regions and suggest that microweathering has had relatively little impact on holocene landscape evolution weathering rind thickness was found to be less on fracture walls than on exposed bedrock surfaces suggesting fractures have not played a significant role in microweathering observations of weathering morphology reveal a range of forms including shallow spalling tafoni and pseudokarren indicating locally intense weathering activity analysis of interrelationships between multiple weathering indices points to the importance of bedrock microweathering as a precursor to macro breakdown and landform evolution the research reasserts the importance of chemical activity in cold environments and the importance of moisture supply for effective microweathering the geological society publishing house 2009

seasonal variations in the geochemistry of shallow groundwater hosted in granitic till the groundwater chemistry in a small catchment in northern sweden has been studied for a period of 15 months including two snowmelt events the groundwater was sampled from two wells in a slope

clay mineralogy of weathering rinds and possible implications concerning the sources of clay minerals in soils weathering rinds on volcanic clasts in quaternary deposits in the western united states contain only very fine grained and poorly crystalline clay minerals rinds were sampled from soils containing well developed argillic b horizons in deposits about 105 yr old or more the clay size fraction of the rinds is dominated by allophane and iron hydroxy oxides whereas the b horizons contain abundant well crystallized clay minerals the contrast between the clay mineralogy of the weathering rinds in which weathering is isolated from other soil processes and that of the associated soil matrices suggests a need to reassess assumptions concerning the rates at which clay minerals form and the sources of clay minerals in argillic b horizons this study suggests that crystalline clay minerals form more slowly in weathering rinds than is generally assumed for soil environments and that the weathering of primary minerals may not be the dominant source of crystalline clay minerals in middle to late pleistocene soils

the role of alluvial fans in the mountain fluvial systems of southeast spain implications of climatic change the mountain fluvial systems of southeast spain involve sediment supply from steep mountain slopes into headwater channels alluvial fans often occur where these headwater channels emerge from the mountain areas and may influence the connectivity of the sediment transport system from the mountain source areas to the main lowland drainages critical in this role is whether the alluvial fans are aggrading or dissecting and whether there is a break or continuity in the channel through the fan environment previous work has identified some of the factors influencing the behaviour of the alluvial fans in southeast spain this paper deals with the mountain front alluvial fans in the semi arid areas of murcia and almeria provinces it attempts by mapping the location of alluvial fans then their classification into aggrading or dissecting fans to identify the extent to which the mountain fluvial systems are buffered by aggrading alluvial fans or exhibit channel continuity through the mountain front environment it further considers the implications of climatically induced changes between aggradational and dissectional behaviour on alluvial fans

cold surface layer thinning on storglaciaren sweden observed by repeated ground penetrating radar surveys 1 a characteristic feature of ground penetrating radar gpr surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface cts hence providing a possible tool for mapping thermal structure with high accuracy comparison of detailed temperature measurements in bore holes and gpr profiles at 345 mhz and 800 mhz center frequencies on storglaciaren sweden show that the cts can be detected and mapped with an accuracy of about 1 m at both frequencies a comparison between comprehensive gpr surveys of the cold surface layer separated by 12 years 1989 2001 shows a substantial and complex thinning of the cold layer an overall decrease of 8 3 m 22 of average thickness of the cts depth is much larger than uncertainties in cts depth determinations the stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of cts there is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning however small increase in average winter air temperature a limiting factor for the temperature gradient through the cold surface layer may provide a partial explanation the weaker temperature gradient reduces the transport of latent heat from the cts thus slowing down its downward migration

estimating ages of late quaternary stream terraces from analysis of weathering rinds and soils rates of growth of rock weathering rinds and rates of changes of soil morphologic and chemical properties that are calibrated at sites of known ages produce powerful tools for estimating ages of geomorphic surfaces particularly when materials datable by conventional methods are not widespread sequences of latest quaternary stream terraces from the south island of new zealand are ideally suited for application of these calibrated age techniques because climate and source materials for terrace deposits are internally consistent within two regions west land and marlborough modal and mean thicknesses of weathering rinds formed in surface cobbles of torlesse graywacke provide age estimates for latest pleistocene and holocene stream terraces in marlborough with uncertainties estimated at 5 to 40 modal rind thickness of subsurface cobbles provides age estimates for latest quaternary westland sites with uncertainties of 10 to more than 50 few dated soils are available to constrain rates of soil development in westland and marlborough furthermore soils were sampled from only one pedon on each surface morphologic data however provide least squares age estimates for westland sites with uncertainties typically greater than 100 and the calibration data can further bracket likely soil ages to less than 50 uncertainty the regression data from marlborough are less reliable but profile index ratios help bracket ages to at least 50 distributions of oxalate extractable fe and ai and total major element concentrations allow age estimates for westland and marlborough soils with uncertainties estimated at 15 to 50 despite these uncertainties the three techniques combine to provide age estimates with the high resolution needed to examine details of fault slip rates or stream downcutting the calibration data and weathering rates used herein are applicable only to the new zealand region studied although similar calibrated age techniques should provide high resolution dating in many other regions such techniques are particularly useful when multiple approaches are available to provide independent cross checks

the role of biological weathering in periglacial areas a study of weathering rinds in south iceland the importance of biogeochemical processes in the morphogenic system of periglacial environments has been underestimated for decades weathering rind studies help to characterise and quantify biogeochemical weathering over time experiments using fungi strains isolated from basaltic boulders allow one to decipher biological weathering a historical approach using heterochronous moraines provides the opportunity to follow the life of weathering rinds and helps to build a chronology of dominant processes of weathering during the first century of exposure it appears that exfoliation of weathering rinds commonly observed on boulders is the result of a combination of both biogeochemical and physical processes

the impact of quaternary sea level and climatic change on coastal alluvial fans in the cabo de gata ranges southeast spain conventionally a fall in base level is seen as stimulating incision into the distal zones of alluvial fans in the cabo de gata ranges of southeast spain evidence exists to the contrary two sets of quaternary coastal alluvial fans demonstrate the interaction between climatically driven variations in the supply of sediment and eustatically driven changes in base level the fans are supplied from miocene volcanic terrain within which no evidence can be found for major tectonic deformation during the period of fan development the evolution of the east coast fans has been affected by variations in sediment supply and changes in sea level the west coast fans were buffered from the effects of changes in sea level by coastal barriers three phases of past sedimentation can be identified on the fans these can be differentiated on the basis of field observations of soil profiles particularly colour of the b horizons and accumulation of caco3 and laboratory analyses of sequential iron oxide extractions and magnetic mineral properties the two earlier major sedimentation phases were coincident with global glacials ca 135 ka and ca 85 10 ka based on the stratigraphy and uranium thorium dating of the coastal sediments high sea levels during the intervening interglacial and during the holocene caused erosion of the distal zones of the east coast fans which led to channel incision into the fan surfaces on the west coast fans no such incision occurred simply proximal incision by small fanhead trenches the youngest relatively minor phase of fan sedimentation has occurred during the holocene these contrasting contexts have produced differing styles of fans with telescopic fan morphology on the east coast and stacked morphology on the west coast fans the differences are reflected in the fan profiles with steeper gradients dominating the east coast fans and extensive lower gradient distal surfaces on the west coast fans fan morphometry based on analysis of the residuals from drainage area to fan area and gradient regressions also differentiates between the fan contexts the fan building phases appear to be controlled proximally by climatically driven pulses of sediment supplied to the fans these occurred during global glacials coincident with low sea levels and caused fan progradation onto the exposed foreshore the intervening global interglacials were times of little fan sedimentation and on the east coast where high sea levels were able to erode the fan toes deep through fan dissection ensued

temporal isotopic variations of dissolved silicon in a pristine boreal river abstract it has previously been concluded that the stable si isotopes are fractionated during geochemical and biogeochemical elemental transfers such as weathering and precipitation of clays and biogenic si which has opened up the possibility of using si as a tracer in natural terrestrial ecosystems furthermore quantification of the biogenic impact on the biogeochemical si cycle has attracted significant scientific interest since biological control has been suggested previous observations of seasonal variations in the dissolved si isotopic pattern further imply that high frequency riverine sampling during main hydrological events might provide important information about natural processes governing the fluvial biogeochemical si cycle therefore temporal variations in the isotopic composition of riverine dissolved si were investigated for the kalix river northern sweden the largest pristine river system in europe based on high frequency sampling during a period of 25 weeks from early april to early october 2006 temporal variations spanning 0 4 for 29si and 0 8 for 30si of dissolved si in the kalix river were observed during the period suggesting that the riverine dissolved si input to the oceans cannot be considered to have a constant si isotopic composition on a short time scale the results implicate biogeochemical si cycling via formation and dissolution of biogenic silica as processes significantly affecting the dissolved si transport in boreal systems during april to early october the si budget in the river system appeared to be controlled by relative si enrichment during high discharge events and relative si depletions in the subarctic mountainous and lake dominated areas the si enrichments and depletions were accompanied by decreasing and increasing riverine 29si and 30si respectively these isotope variations can be explained by release of plant derived silica depleted in heavier si isotopes during the spring snowmelt further increased volumetric contribution from the headwater and losses of dissolved si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes as further verified by land cover analysis

temporal and spatial variations of rock weathering and co2 consumption in the baltic sea catchment this study provides the first estimate of silicate and carbonate weathering rates and derived co2 consumption rates for the baltic sea catchment using river chemistry data of 78 rivers draining int

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

a porosity related diffusion model of weathering rind development abstract a model of weathering rind growth is proposed based on the study of andesite cobbles sampled from a modern floodplain and four fluvial terraces 0 20 130 290 and 660 ka in central japan the times elapsed since each of the above ages can be assumed to be the weathering periods the 0 ka rocks are not visibly weathered the 20 ka rocks have an alteration layer with white or brown colours and a mean thickness of 0 7 mm on their surface the 130 290 and 660 ka rocks have brown weathering rinds with average thicknesses of 3 6 mm based on the measurements of physical and mechanical properties throughout from the rock surface to the interior weathering rinds are divided into two bands the outer brown band is characterized by ferric hydroxides which experienced both oxidization and leaching the inner band is formed by leaching alone of alkalis alkaline earths the inner border of this band is located at the position where vickers hardness numbers start decreasing with decreasing depth the thickness of each band was determined from its physical and mechanical properties the results show that brown band thickness l i is a function of time however total thickness of the two bands i e total weathering rind thickness l i ii is also controlled by initial rock porosity n their relationships are represented by diffusive equations l i dt 1 2 0 0283 t 1 2 and l i ii dt 1 2 0 0431 exp 0 4287 n t 1 2 these findings indicate that rind characterization and original rock porosity should be taken into consideration when weathering rind thickness is used as a dating tool

in situ weathering rind erosion abstract the use of cosmogenic nuclide dating methods place in doubt the long term future of weathering rinds wrs as a chronometric tool why estimate ages when radiometric control is possible this paper presents evidence that wrs can provide invaluable clues about what particular sample would provide the most accurate cosmogenic age by avoiding inheritance of cosmogenic nuclides and by avoiding boulders undergoing spalling the key to this new use requires testing the occurrence and nature of wr erosion back scattered electron microscopy reveals that ignimbrite andesite basalt and granitic clasts experience wr erosion in all subsurface and surface contexts thus far studied in arizona california hawaii oregon and washington to understand the magnitude of wr erosion we measured wr thicknesses all while controlling the cosmogenic and surface stability ages of clasts by chlorine 36 and rock varnish microlamination dating methods our data reveal that traditional methodologies of sampling cobbles remove two thirds of the true thickness of weathering rinds calling into question many beliefs including the notion that clay minerals are not produced during weathering rind formation comparisons of optical and electron microscope measurements support concerns that measurement of wrs by color changes while useful as a pedagogical tool creates serious biases in underestimating the true dynamics of wrs in the end we found that concordance of wr and rock coating age trends indicates the ideal boulder for cosmogenic nuclide dating offsets reveal either ongoing boulder erosion invalidating zero erosion model ages or a potential problem with inheritance of cosmogenic nuclides

importance of weathering and human perturbations on the riverine transport of si the global si cycle is strongly controlled by riverine input over the last decade two parameters have been shown to play a significant role in the control of dissolved si dsi biology through the effects of diatom blooms and vegetation growth and human activity through the effects of eutrophication urbanisation agriculture deforestation and damming human perturbations should now be better quantified when modelling the global si cycle and particularly in the tropics a case study is presented based on preliminary data along the kaveri river india strongly impacted by dams it is suggested that dsi is controlled by a combined effect of chemical weathering damming and groundwater recharge

the fluvial geochemistry contributions of silicate carbonate and saline alkaline components to chemical weathering flux and controlling parameters narmada river deccan traps india abstract the narmada river in india is the largest west flowing river into the arabian sea draining through the deccan traps one of the largest flood basalt provinces in the world the fluvial geochemical characteristics and chemical weathering rates cwr for the mainstream and its major tributaries were determined using a composite dataset which includes four phases of seasonal field spot samples during 2003 and 2004 and a decade long 1990 2000 fortnight time series multiannual data here we demonstrate the influence of minor lithologies carbonates and saline alkaline soils on basaltic signature as reflected in sudden increases of ca2 mg2 and na contents at many locations along the mainstream and in tributaries both spot and multiannual data corrected for non geological contributions were used to calculate the cwr the cwr for spot samples cwrspot vary between 25 and 63 ton km 2 year 1 showing a reasonable correspondence with the cwr estimated for multiannual data cwrmulti at most study locations the weathering rates of silicate silwr carbonate carbwr and evaporite sal alkwr have contributed 38 58 28 45 and 8 23 respectively to the cwrspot at different locations the estimated silwr 11 36 ton km 2 year 1 for the narmada basin indicates that the previous studies on the north deccan rivers narmada tapti godavari overestimated the silicate weathering rates and associated co2 consumption rates the average annual co2 drawdown via silicate weathering calculated for the narmada basin is 0 032 1012 moles year 1 suggesting that chemical weathering of the entire deccan trap basalts consumes approximately 2 0 24 1012 moles of the annual global co2 drawdown the present study also evaluates the influence of meteorological parameters runoff and temperature and physical weathering rates pwr in controlling the cwr at annual scale across the basin the cwr and the silwr show significant correlation with runoff and pwr on the basis of observed wide temporal variations in the cwr and their close association with runoff temperature and physical erosion we propose that the cwr in the narmada basin strongly depend on meteorological variability at most locations the total denudation rates tdr are dominated by physical erosion whereas chemical weathering constitutes only a small part

mongolian summits an uplifted flat old but still preserved erosion surface in gobi altay and altay mongolia several flat surfaces worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m suggests disruption of a single large scale surface new thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during jurassic time the gobi altay and altay flattopped massifs are tectonically and geomorphologically unique their preservation for 150 m y implies that no further tectonic movements occurred before the onset of the last deformation episode 5 3 m y ago it also suggests that very low erosion rates were maintained by a dry climate over millions of years

morphological dating of cumulative reverse fault scarps examples from the gurvan bogd fault system mongolia summary we relate reverse fault scarp morphology formed by several earthquake dislocations to the average deformation rate using a morphological dating model based on a diffusion analogue of erosion our scarp degradation model includes diffusive erosion during the interseismic period the gravitational collapse of the coseismic fault scarp just after formation and the variation of the surface rupture location interactions between thrusting and geomorphic processes acting on scarp morphology are analysed along the gurvan bogd range in mongolia four main processes acting on scarp morphology were distinguished i gravitational collapse of the frontal scarp resetting the diffusive scarp if fault offsets are big and faulting is localized 2 progressive erosion of the fault scarp during the interseismic period 3 folding associated with the frontal thrust and backthrusts 4 competing alluvial deposition on mountain piedmont slopes and abrasion of the fault scarp by wash processes the growth of cumulative reverse fault scarps is suppressed when they are located in the outwash of major drainage basins they can grow higher in distance from major catchment discharges the modelling suggests that the morphology of the scarp and its apparent degradation stage depend on the parameters controlling the amount of frontal collapse the magnitude of coseismic offsets the dip of the fault near the surface and the step distance between faults folding associated with thrusting creates a convexity on the upper part of the scarp and increases its height the comparison of different scarp profiles suggests that folding leads to an overestimate of the morphological age we estimate a diffusion coefficient at 3 3 1 7 m 2 ka l morphological ages calculated with our model confirm that slip rate along reverse faults of the gurvan bogd range has not been constant over the last 100 ka

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

rock control on microweathering of bedrock surfaces in a periglacial environment abstract microweathering of ice smoothed bedrock surfaces was investigated in the roldal area of hardanger plateau 60 southern norway postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces weathering processes are inferred from assessment of weathering rind formation surface hardness and the preservation of small scale glacial erosional features surface lowering rates for a range of metamorphic rocks vary from 0 05 to 2 20 mm ka 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments the mean rate of surface lowering at 0 55 mm ka 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution variations in bedrock microweathering can be explained by lithological variation amphibolite and mica rich bedrock surfaces experience greater denudation and weakening least weathering rind formation and abundant preservation of glacial striae despite greater surface lowering conversely quartz rich bedrock surfaces are most resistant to denudation and weakening but have greater weathering rind formation and fewer preserved striae postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity granular decomposition is manifest in the formation of weathering rinds analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion a conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages the model proposes that cyclic processes of in situ disintegration decomposition and erosion are at work the relative balance between these processes varies with lithology so that in more resistant quartz rich rocks the net effect is minimal surface lowering and accumulation of weathering rind in weaker amphibolitic and micaceous rocks the net effect is greater surface lowering and minimal accumulation of weathering rind the results of the research demonstrate the important influence of rock properties notably mineral composition in postglacial microweathering of crystalline bedrock in a periglacial environment

ground based and uav based photogrammetry a multi scale high resolution mapping tool for structural geology and paleoseismology this contribution reviews the use of modern 3d photo based surface reconstruction techniques for high fidelity surveys of trenches rock exposures and hand specimens to highlight their potential for paleoseismology and structural geology we outline the general approach to data acquisition and processing using ground based photographs acquired from standard dslr cameras and illustrate the use of similar processing approaches on imagery from unmanned aerial vehicles uavs it is shown that digital map and trench data can be acquired at ultra high resolution and in much shorter time intervals than would be normally achievable through conventional grid mapping the resulting point clouds and textured models are inherently multidimensional x y z point orientation colour texture archival and easily transformed into orthorectified photomosaics or digital elevation models dems we provide some examples for the use of such techniques in structural geology and paleoseismology while pointing the interested reader to free and commercial software packages for data processing visualization and 3d interpretation photogrammetric models serve to act as an ideal electronic repository for critical outcrops and observations similar to the electronic lab book approach employed in the biosciences this paper also highlights future possibilities for rapid semi automatic to automatic interpretation of the data and advances in technology

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

thermal stress weathering and the spalling of antarctic rocks using in situ field measurements laboratory analyses and numerical modeling we test the potential efficacy of thermal stress weathering in the flaking of millimeter thick alteration rinds observed on cobbles and boulders of ferrar dolerite on mullins glacier mcmurdo dry valleys mdv in particular we examine whether low magnitude stresses arising from temperature variations over time result in thermal fatigue weathering yielding slow crack propagation along existing cracks and ultimate flake detachment our field results show that during summer months clasts of ferrar dolerite experience large temperature gradients across partially detached alteration rinds 4 7 c mm 1 and abrupt fluctuations in surface temperature up to 12 c min 1 the latter are likely due to the combined effects of changing solar irradiation and cooling from episodic winds the results of our thermal stress model coupled with subcritical crack growth theory suggest that thermal stresses induced at the base of thin alteration rinds 2 mm thick common on rocks exposed for 105 years may be sufficient to cause existing cracks to propagate under present day meteorological forcing eventually leading to rind detachment the increase in porosity observed within alteration rinds relative to unaltered rock interiors as well as predicted decreases in rind strength based on allied weathering studies likely facilitates thermal stress crack propagation through a reduction of fracture toughness we conclude that thermal stress weathering may be an active though undervalued weathering process in hyperarid terrestrial polar deserts such as the stable upland region of the mdv

prehistoric ruptures of the gurvan bulag fault gobi altay mongolia 1 the 1957 gobi altay m8 3 earthquake in southern mongolia was associated with the simultaneous rupture of several faults including the gurvan bulag reverse fault which is located about 25 km south of the main strike slip bogd fault our study of paleoseismic excavations across the gurvan bulag fault suggests that the penultimate surface rupture occurred after 6 0 ka most likely between 2 6 and 4 4 ka and a possible earlier rupture occurred after 7 3 ka our interpretation of the stratigraphic relations in one of the exposures suggests that at least five earthquakes have generated surface rupture of the gurvan bulag fault since the abandonment of an ancient alluvial fan surface luminescence dating of sediment associated with this surface indicates that it formed either 26 6 2 1 ka or 16 1 2 0 ka these data imply that the recurrence intervals for surface faulting on the gurvan bulag and bogd faults are similar on the order of several thousands of years but that the penultimate surface ruptures of the two faults did not occur during the same earthquake

tectonic and climatic controls on fan systems the kohrud mountain belt central iran abstract late pleistocene to holocene fans of the kohrud mountain belt central iran illustrate the problems of differentiating tectonic and climatic drivers for the sedimentary signatures of alluvial fan successions it is widely recognised that tectonic processes create the topography that causes fan development the existence and position of fans along the kohrud mountain belt ne of esfahan are controlled by faulting along the qom zefreh fault system and associated fault zones these faults display moderate amounts of historical and instrumental seismicity and so may be considered to be tectonically active however fluvial systems on the fans are currently incising in response to low gavkhoni playa lake levels since the mid holocene producing incised gullies on the fans up to 30 m deep these gullies expose an interdigitation of lake deposits dominated by fine grained silts and clays with evaporites and coarse gravels that characterise the alluvial fan sediments the boundaries of each facies are mostly sharp with fan sediments superimposed on lake sediments with little to no evidence of reworking in turn anhydrite glauberite mirabilite and halite crusts drape over the gravels recording a rapid return to still water shallow ephemeral saline lake sedimentation neither transition can be explained by adjustment of the hinterland drainage system after tectonic uplift the potential influence in central iran of enhanced monsoons the northward drift of the intertopical convergence zone itcz and mediterranean climates for the early holocene 6 10 ka point to episodic rainfall during winter months associated with discrete high magnitude floods on the fan surfaces the fan sediments were deposited under the general influence of a highstand playa lake whose level was fluctuating in response to climate this study demonstrates that although tectonism can induce fan development it is the sensitive balance between aridity and humidity resulting from changes in the climate regime of central iran that influences the nature of fan sequences and how they interrelate to associated facies

late cenozoic transpression in southwestern mongolia and the gobi altai tien shan connection the gobi altai region of southwestern mongolia is a natural laboratory for studying processes of active transpressional intracontinental mountain building at different stages of development the region is structurally dominated by several major e w left lateral strike slip fault systems the north gobi altai fault system is a seismically active right stepping left lateral strike slip fault system that can be traced along the surface for over 350 km the eastern two thirds of the fault system ruptured during a major earthquake m 8 3 in 1957 whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the quaternary the highest mountains in the gobi altai are restraining bend uplifts along the length of the fault system detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross sectional geometries with thrust faults rooting into oblique slip and strike slip master faults continued ne directed convergence across the fault system coupled with left lateral strike slip displacements will lead to growth and coalescence of the restraining bends into a continuous sublinear range possibly obscuring the original strike slip fault system this may be a common mountain building process the largely unknown gobi tien shan fault system is a major left lateral strike slip fault system 1200 km long that links the southern ranges of the gobi altai with the barkol tagh and bogda shan of the easternmost tien shan in china active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section indicating quaternary activity the total displacement is unknown but small parallel splays have apparent offsets of 20 km suggesting that the main fault zone has experienced significantly more displacement field investigations conducted at two locations in southwestern mongolia indicate that late cenozoic transpressional uplift is still active along the fault system the spatial relationship between topography and active faults in the barkol tagh and bogda shan strongly suggests that these ranges are large coalescing restraining bends that have accommodated the fault s left lateral motion by thrusting oblique slip displacement and uplift thus from a mongolian perspective the easternmost tien shan formed where it is because it lies at the western termination zone of the gobi tien shan fault system the gobi tien shan fault system is one of the longest fault systems in central asia and together with the north gobi altai and other smaller subparallel fault systems is accommodating the eastward translation of south mongolia relative to the hangay dome and siberia these displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low e w trending corridor between the northern edge of the tibetan plateau and the hangay dome presumably in response to the indo eurasian collision 2500 km to the south

plant induced weathering of hawaiian basalts abstract the rise of rooted upland vascular plants during the devonian probably had a major effect on the rate of weathering of silicate rocks and consequently on levels of atmospheric co2 at that time in order to better understand the role of plants in rock weathering an electron microscope microprobe study of the root rock interface has been done on several young 100 3000 year old hawaiian basalts we observe the development of porosity due to dissolution of minerals by solutions secreted by symbiotic microbiota associated with plant roots in nearby plant free parts of the same basalt flows similar porosity development is essentially absent also in nearby areas covered by lichens the extent of rock dissolution is much less in these early stages of weathering dissolution is complete and voids are not infilled by fine grained weathering products quantitative measurement of porosity around roots developed on flows of known age enables the calculation of a rate of basalt weathering that is in order of magnitude agreement with results based on the study of global volcanic weathering based on the chemistry of river water

source history of the 1905 great mongolian earthquakes tsetserleg bolnay summary two great mongolian earthquakes tsetserleg and bolnay occurred on 1905 july 9 and 23 we determined the source history of these events using body waveform inversion the tsetserleg rupture azimuth n60 correspond to a n60 oriented branch of the long ew oriented bolnay fault historical seismograms recorded by wiechert instruments are digitized and corrected for the geometrical deformation due to the recording system we use predictive filters to recover the signals lost at the minute marks the total rupture length for the tsetserleg earthquake may reach up to 190 km in order to explain the width of the recorded body waves this implies adding 60 km to the previously mapped fault the rupture propagation is mainly eastward it starts at the southwest of the central subsegment showing a left lateral strike slip with a reverse component the total duration of the modelled source function is 65 s the seismic moment deduced from the inversion is 1021 n m giving a magnitude mw 8 the nucleation of the bolnay earthquake was at the intersection between the main fault 375 km left lateral strike slip and the teregtiin fault n160 80 km long right lateral strike slip with a vertical component near the main fault the rupture was bilateral along the main fault 100 km to the west and 275 km to east it also propagated 80 km to the southeast along the teregtiin fault the source duration was 115 s the moment magnitude mw varies between 8 3 and 8 5 the nucleation and rupture depths remain uncertain we tested three cases 1 nucleation and rupture depth limited to the seismogenic zone 2 nucleation in the seismogenic zone and rupture propagation going to the base of the crust and 3 nucleation within the crust upper mantle interface and rupture propagation within the upper mantle

durability of soft rocks in eocene flysch formation dalmatia croatia abstract the mechanical weathering of marl in the form of disintegration of intact material caused by repeated drying and wetting also known as slaking is an important factor affecting the durability and stability of cuts in soft rocks and eocene flysch formations dalmatia croatia it is often valued and used in rock classification as a slake durability index sdi an index property recommended by the international society for rock mechanics and american society for testing and materials it was observed that the results of conventional laboratory tests on marl samples using two slaking cycles are not always in accordance with the appearance of the samples after testing highly fragmented rock material in spite of the high resistance durability result based on the retained sample mass depending on factors such as porosity hydraulic conductivity and mineralogical composition the effects of weathering might sometimes not be obvious within two cycles which suggested that durability classification is not suitable for all soft rock types in order to determine the additional criteria that would reduce the uncertainty of standardised durability testing in soft rocks both the standard and modified tests of durability as well as a series of additional index tests carbonate content dry density water absorption porosity and point load strength index were conducted on 70 samples of marl several variants of the sdi were analysed with various numbers of cycles cycle times and combinations thereof to emphasise the differences between various types of marl a variant of loss slake index was introduced and determined using 30 samples based on the results obtained according to the degradation type observed after the slaking the samples were grouped into three groups based on the presented results a classification with the defined criteria for high medium and low durability has been suggested for the purpose of a durability analysis of the cuts in marls

a reactive transport model for weathering rind formation on basalt abstract saprolite formation rates influence many important geological and environmental issues ranging from agricultural productivity to landscape evolution here we investigate the chemical and physical transformations that occur during weathering by studying small scale saprolites in the form of weathering rinds which form on rock in soil or saprolite and grow in thickness without physical disturbance with time we compare detailed observations of weathered basalt clasts from a chronosequence of alluvial terraces in costa rica to diffusion reaction simulations of rind formation using the fully coupled reactive transport model crunchflow the four characteristic features of the weathered basalts which were specifically used as criteria for model comparisons include 1 the mineralogy of weathering products 2 weathering rind thickness 3 the coincidence of plagioclase and augite reaction fronts and 4 the thickness of the zones of mineral reaction i e reaction fronts four model scenarios were completed with varying levels of complexity and degrees of success in matching the observations to fit the model to all four criteria however it was necessary to 1 treat diffusivity using a threshold in which it increased once porosity exceeded a critical value of 9 and 2 treat mineral surface area as a fitting factor this latter approach was presumably necessary because the mineral water surface area of the connected accessible porosity in the costa rica samples is much less than the total porosity navarre sitchler et al 2009 the model fit surface area here termed reacting surface area was much smaller than the bet measured surface area determined for powdered basaltic material in the parent basalt reacting surface area and diffusivity are low due to low pore connectivity and early weathering is therefore transport controlled however as pore connectivity increases as a result of weathering the reacting surface area and diffusivity also increase and weathering becomes controlled by mineral reaction kinetics the transition point between transport and kinetic control appears to be related to a critical porosity 9 at which pore connectivity is high enough to allow rapid transport based on these simulations we argue that the rate of weathering front advance is controlled by the rate at which porosity is created in the weathering interface and that this porosity increases because of mineral dissolution following a rate that is largely surface reaction controlled

a 900 k y record of strath terrace formation during glacial interglacial transitions in northwest china the timing of the development of strath terraces with respect to climatic variability remains equivocal previous studies attribute strath terrace formation to glacial or interglacial climates or to variations in sediment and water fluxes that cause lateral erosion followed by vertical incision a chronology of strath terrace formation spanning similar to900 k y has been generated on the basis of loess paleosol couplets and paleomagnetic thermoluminescence and radiocarbon dating of strath terraces in the qilian shan of northeastern tibet repetitive stratigraphic and geomorphic patterns on each terrace indicate that they formed during glacial interglacial transitions long term bedrock incision rates and inferred rock uplift rates appear steady and unrelated to strath formation over the past 900 k y

relic permafrost structures in the gobi of mongolia age and significance relict permafrost structures ice wedge casts and cryoturbation structures are present in the gobi of southern mongolia luminescence dates of sediments are presented to constrain the age of formation of permafrost structures these data show that there was a phase of permafrost development during the latter part of the last glacial after about 22 to 15 ka that resulted in cryoturbated sediments and ice wedge casts furthermore permafrost degradation occurred during late pleistocene times 13 10 ka and was absent during the early holocene these permafrost structures mark the southernmost evidence of permafrost in northern asia during late quaternary times and indicate that the mean annual air temperature was below approximately 6 c during their formation 1998 john wiley sons ltd

timing of formation of forebergs in the northeastern gobi altai mongolia implications for estimating mountain uplift rates and earthquake recurrence intervals bedrock and quaternary alluvial fans in the forelands of the northern gobi altai have been faulted and warped by foreland propagating thrust faults to form elongate hills known as forebergs forebergs near bogd town north of arsta bogd and at ih hetsuu north of baga bogd were mapped and their formation constrained using luminescence dating of lacustrine and fanglomerates sediments to give localized uplift rates of c 0 05 m ka 1 and between c 1 6 and 4 1 m ka 1 respectively comparisons between vertical surface rupture during the 1957 gobi altai earthquake with the age and amount of uplift of lacustrine sediments provide a tentative estimate of between 1288 382 to 497 120 years for the average recurrence interval of great earthquakes in the baga bogd region these localized uplifts rates support the view that the gobi altai mountains probably took between 50 and 25 million years to form and were therefore coeval with the uplift of the himalayas and the tibetan plateau

the effect of organic matter on chemical weathering study of a small tropical watershed nsimi zoetele site cameroon abstract the effect of organic matter during soil water interaction is still a debated issue on the controls of chemical weathering in a tropical environment in order to study this effect in detail we focused on the weathering processes occurring in a small tropical watershed nsimi zoetele south cameroon this site offers an unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry the lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones unsaturated slope soils on the hills and or elevated areas and water saturated soils in the swamp zone which represent 20 of the basin surface the study present chemical analysis performed on water samples collected monthly from different localities between 1994 1997 and on soil samples taken during a well drilling in december 1997 the results suggest the existence of chemical and spatial heterogeneities of waters in the basin colored waters flooding the swamp zone have much higher concentrations of both organic matter i e doc and inorganic ions e g ca mg al fe th zr than those from springs and groundwater from the hills nevertheless these organic rich waters present cation concentrations na ca mg k which are among the lowest compared to that of most world rivers the main minerals in the soils are secondary kaolinite iron oxi hydroxides quartz and accessory minerals e g zircon rutile we mainly focused on the mineralogical and geochemical study of the swamp zone soils and showed through sem observations the textural characterization of weathered minerals such as kaolinite zircon rutile and the secondary recrystallization of kaolinite microcrystals within the soil profile water chemistry and mineralogical observations suggest that hydromorphic soils of the swamp zone are responsible for almost all chemical weathering in the basin thus in order to explain the increase of element concentration in the organic rich waters we suggest that organic acids enhance dissolution of minerals such as kaolinite goethite and zircon and also favors the transport of insoluble elements such as al fe ti zr and ree by chemical complexation sio2 aq concentrations in these waters are above saturation with respect to quartz dissolution of phytholithes amorphous silica may be responsible for this relatively high sio2 aq concentration al mg ratios obtained for the soil and the mengong river waters show that a significant amount of al does not leave the system due to kaolinite recrystallisation in the swamp zone soils geochemical data obtained for this watershed show the important contribution of vegetation and organic matter on chemical weathering in the swamp zone quantitatively we propose that the increasing amount in total dissolved solid tds due to organic matter and vegetation effect is about 35 in summary this interaction between soils and waters occurs mostly in soils that are very depleted in soluble elements thus the low concentration of major elements in these water is a direct consequence of the depleted nature of the soils

geomorphological analysis of neotectonic deformation northern owens valley california at the western edge of the basin and range province the owens valley is the site of active seismicity and deformation morphometric analyses of three geomorphological features are used to determine the patterns and rates of neotectonic deformation l a network of pleistocene channels cut on top of the bishop tuff 2 uplifted terraces of the owens river and 3 alluvial fans of the white mountain front

the role of base level change in the dissection of alluvial fans case studies from southeast spain and nevada abstract tectonics climate and base level are the underlying controls of alluvial fan development on many fans base level is stable but where base level change occurs it may itself be a response to tectonics or climatic change tectonically induced base level change will be temporally independent of climatic change and will show spatial variability depending on the rate of propagation of tectonically induced regional dissection this is illustrated by the tabernas fans southeast spain the timing of climatically induced base level change follows the timing of climatic change itself and will show more consistency of spatial relationships within groups of fans affected alluvial fans which toe out in coastal zones or at lake shorelines may be influenced by climatically controlled base level changes conventionally a fall in base level would be expected to cause dissection of the distal fan zone however the reverse may occur with fan progradation taking place in response to a base level fall and dissection occurring in response to a base level rise two contrasted case studies are considered based in part on previously published work from dry region alluvial fan zones the coastal cabo de gata fans in southeast spain and the stillwater and cold springs fans in nevada usa in these areas base level changes occurred in response to late quaternary eustatic changes of sea level and changes in the levels of pluvial lakes respectively within both areas there are fans not affected by base level change cabo de gata west coast and inland fans cold springs fans and others where base level change has been important in fan evolution cabo de gata east coast fans stillwater fans the differences in geomorphic regime between those fans influenced by base level changes and those not are expressed in morphometric contrasts and different fan profile and plan characteristics within those fans influenced by base level changes the different mechanisms have influenced the location and elevation of the zone of incision the differences can be attributed in part to the temporal interactions of base level change with climatically induced changes in sediment supply and in part to differences in gradients of the foreshore exposed by the falling sea or lake base levels

enhanced chemical weathering of rocks during the last glacial maximum a sink for atmospheric co2 abstract it has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric co2 on the continents may have at least partly contributed to the low co2 concentrations during the last glacial maximum lgm variations in continental erosion could thus be one of the driving forces for the glacial interglacial climate cycles during quaternary times to test such an hypothesis a global carbon erosion model has been applied to a lgm scenario in order to determine the amount of co2 consumed by chemical rock weathering during that time in this model both the part of atmospheric co2 coming from silicate weathering and the part coming from carbonate weathering are distinguished the climatic conditions during lgm were reconstructed on the basis of the output files from a computer simulation with a general circulation model only the predicted changes in precipitation and temperature have been used whereas the changes in continental runoff were determined with an empirical method it is found that during the lgm the overall atmospheric co2 consumption may have been greater than today by about 20 mainly because of greater carbonate outcrop area related to the lower sea level on the shelves this does not however affect the atmospheric co2 consumption by silicate weathering which alone has the potential to alter atmospheric co2 on the long term silicate weathering and the concomitant atmospheric co2 consumption decreased together with a global decrease of continental runoff compared to present day both by about 10 nevertheless some uncertainty remains because the individual lithologies of the continental shelves as well as their behavior with respect to chemical weathering are probably not well enough known the values we present refer to the ice free continental area only but we tested also whether chemical weathering under the huge ice sheets could have been important for the global budget although glacial runoff was considerably increased during lgm weathering under the ice sheets seems to be of minor importance

weathering plants and the long term carbon cycle the chemical weathering of ca mg silicate rocks is the principal process whereby co2 is removed from the atmosphere on long or multimillion year time scales at present vascular land plants exert an important influence on weathering by recycling water and by bringing about the secretion of acids and the buildup of high levels of co2 in soils before the spread of vascular plants on the continents during the mid paleozoic chemical weathering must have been achieved by higher levels of atmospheric co2 and or by the intercession of primitive land biota such as lichens and cyanobacteria from examination of several pre vascular weathering scenarios it is concluded that in order to prohibit unreasonably high levels of atmospheric co2 weathering during the precambrian and early paleozoic must have taken place under essentially closed system abiotic conditions linear feedback or via strong regulation by primitive biota preliminary examination of modern weathering by lichens over tens to thousands of years militates against the latter possibility however much more work needs to be done on the quantitative effect of both primitive biota and vascular plants on the rate of weathering and their response to changes in atmospheric co2 before anything more definitive can be said

a very efficient o n implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution abstract we present a new algorithm to solve the basic stream power equation which governs channel incision and landscape evolution in many geomorphic settings the algorithm is highly efficient because computation time increases linearly with the number of points used to discretize the landscape and is ideally suited to parallelization it is also unconditionally stable because it uses an implicit scheme for the time integration of the landscape evolution equation which means that large time steps can be used without sacrificing accuracy in this paper we describe the algorithm and present results that demonstrate its efficiency and accuracy

active intracontinental transpressional mountain building in the mongolian altai defining a new class of orogen abstract mountain ranges that are actively forming around the western and northern perimeter of the indo eurasia collisional deformational field such as the mongolian altai comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens late cenozoic uplift and mountain building in the mongolian altai is dominated by regional scale dextral strike slip faults that link with thrust and oblique slip faults within a 300 km wide deforming belt sandwiched between the more rigid junggar basin block and hangay precambrian craton dominant orogenic elements in the mongolian altai include double restraining bends terminal restraining bends partial restraining bends single thrust ridges thrust ridges linked by strike slip faults and triangular block uplifts in areas of conjugate strike slip faults the overall pattern is similar to a regional strike slip duplex array however the significant amount of contractional and oblique slip displacement within the range and large number of historical oblique slip seismic events renders the term transpressional duplex more accurate intramontane and range flanking basins can be classified as ramp basins half ramp basins open sided thrust basins pull apart basins and strike slip basins neither a classic fold and thrust orogenic wedge geometry nor a bounding foredeep exists the manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown however crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late cenozoic regional epeirogenic uplift in the russian altai and sayan regions

effect of porosity on the increase in weathering rind thicknesses of andesite gravel abstract factors affecting the increase in weathering rind thickness i e weathering rates were investigated using andesite gravel in fluvial terrace deposits with a known emergence time the time between the age of each terrace formation 20 130 290 and 660 ka and the present was assumed to be the weathering period three zones were classified from measurements of the vickers hardness number vhn across weathering rinds from the rock surface to the inner fresh part 1 zone i the outermost brown layer which has low vhn values of 10 to 80 gf m2 2 zone ii the inner gray layer which has increasing vhn values 100 to 500 gf m2 with increasing depth 3 the innermost fresh part which has large vhn values of 500 gf m2 in this paper zones i and i ii are defined as the brown layer and the weathering rind respectively diffusion theory was applied to the relationship between the thickness of the brown layer or the weathering rind and time weathering periods the results show that the thickness of the brown layer depends mainly on time whereas the thickness of the weathering rind is controlled by the porosity of the host rock as well as time consequently rocks with higher porosity have thicker weathering rinds than brown layers

transpressional tectonics and stream terraces of the gobi altay mongolia we studied the patterns rates and evolution of fluvial terraces and fault system during the building process of an intracontinental transpressional mountain in the gobi altay mongolia by analyzing incisions and offsets of fluvial terraces and alluvial fans we show that the massif has grown by outward migration of thrust faults through time on the northern flank the present bounding thrust fault began its activity 600 ka ago while a more internal sub parallel fault was still active until 200 100 ka vertical offset of an alluvial fan abandoned 100 ka ago allows an estimate of 0 1 mm yr upper pleistocene holocene uplift rate the morphology of the catchment piedmont system strongly suggests a periodical formation of the alluvial surfaces controlled by the climatic pulses at the beginning of the wet interglacial periods the abandonment of the alluvial terraces lags by several thousand years the abandonment of the alluvial fans showing a diachronous incision propagating upstream the incision rate deduced from the different elevations of straths exceeds of one order of magnitude the rock uplift rate this excess is mostly due to ongoing drainage network growth at the core of the massif and incision due to alluvial apron entrenchment near the outlet this implies that fluvial response is mainly controlled by drainage growth interaction with piedmont and cyclic climatic variations rather than by rock uplift

changes in the hypsometric curve through mountain building resulting from concurrent tectonics and denudation abstract the stages of geomorphic development of mountains have sometimes been explained based on strahler s diagram of hypsometric curves although the japanese mountains are young they do not follow his diagram hypsometric curves simulated using empirical laws deduced from the japanese mountains indicate that mountain building resulting from concurrent tectonics and denudation does not produce convex curves but concave and or s shaped curves the hypsometric curve of a mountain changes from a concave curve to an s shaped curve in accordance with the increase in mountain altitude the succession of the hypsometric curve during concurrent tectonics and denudation is the reverse of strahler s diagram the hypsometric integral increases with the advance in stage which is evaluated based on the change in mountain altitude it has a relatively good correlation with the stage however the sequence of change in the hypsometric integral is different according to the extent of the terrain examined whether the terrain is restricted to the interior of a mountain or pertains to the whole mountain and whether it includes newly emerged land the stage should be evaluated based on the course of change in the integral characteristics for the extent of the mountain examined

control of geomorphic processes on 10be concentrations in individual clasts complexity of the exposure history in gobi altay range mongolia the dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre deposition inheritance from the post deposition history of the clasts in the studied marker moreover estimating catchment scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local regional relationships between rock exhumation and transport through space and time this is still poorly known for timescales of tens of thousand years in order to document the evolution of clast exhumation and transport rates through time we analyze in situ 10be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in gobi altay mongolia strongly affected by global climatic changes during the pleistocene holocene period samples were collected on bedrock abandoned alluvial deposits active colluvia and alluvia our results show a large 10be scattering in the active river bed consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision on the contrary pre exposure signal within abandoned terraces is much more homogeneous consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport these results show that exhumation transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations the occurrence of abrupt climatic changes during short periods of time recorded by 10be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers on the other hand strong and short erosion events limit and homogenize the pre exposure 10be signal in associated deposits like debris flows making them particularly suitable markers for dating in active tectonic and paleoclimatic studies

weathering rinds as mirror images of palaeosols examples from the western alps with correlation to antarctica and mars weathering rinds have been used for decades as relative age indicators to differentiate glacial deposits in long quaternary sequences but only recently has it been shown that rinds contain long and extensive palaeoenvironmental records that often extend far beyond mere repositories of chemical weathering on both earth and mars when compared with associated palaeosols in deposits of the same age rinds often carry a zonal weathering record that can be correlated with palaeosol horizon characteristics with respect to both abiotic and biotic parameters as demonstrated with examples from the french and italian alps rinds in coarse clastic sediment contain weathering zones that correlate closely with horizon development in associated palaeosols of presumed late glacial age in addition to weathering histories in both rinds and palaeosols considerable evidence exists to indicate that the black mat impact 12 8 ka reached the european alps a connection with the younger dryas readvance supported by both mineral and chemical composition preliminary metagenomic microbial analysis using density gradient gel electrophoresis suggests that the eubacterial microbial population found in at least one ah palaeosol horizon associated with a rind impact site is different from that in other late glacial and younger dryas surface palaeosol horizons

hydrological alterations with river damming in northern sweden implications for weathering and river biogeochemistry hydrological alterations with river damming in northern sweden implications for weathering and river biogeochemistry

weathering rind formation in buried terrace cobbles during periods of up to 300ka abstract weathering rinds formed in mesozoic sandstone and basalt cobbles buried in terrace deposits for up to 300 ka have been investigated the aim was to determine the formation process and elemental mass balances during rind development the ages of terraces distributed in the western part of fukui prefecture central japan have been determined as 50 ka 120 ka and 300 ka based on a tephro stratigraphic method detailed investigations across the weathering rinds consisting of microscopic observations porosity measurements and mineralogical and geochemical analyses using x ray diffractometry xrd x ray fluorescence xrf secondary x ray analytical microscopy sxam scanning electron microanalyser sem and electron probe microanalysis epma have been carried out the results revealed that the fe concentrations in the weathering rind of a basalt cobble slightly decreased from the cobble s surface rim towards the unweathered core in contrast in a sandstone cobble formed under the same environmental conditions over the same period of time there is an fe rich layer at some distance below the cobble s surface elemental mass balances across the rinds were determined by using open system mass balance i j calculations and show that the fe was precipitated as fe oxyhydroxides in the basalt cobbles although fe was slightly removed from the rims in sandstone cobbles on the other hand fe migrated along a fe concentration gradient by diffusion and precipitated as fe oxyhydroxide minerals to form the weathering rinds presumably precipitation was due to the relatively higher ph conditions caused by mineral dissolution within the pores principally involving calcite but probably also silicates including feldspar the detailed characterization of the weathering rinds revealed the influence of lithology on the accumulation and dissolution of fe oxyhydroxides causing weathering rinds with different characteristics to develop in different kinds of buried cobbles under the same conditions relatively large climatic changes in the study area did not cause discernable variations in the mean formation rates of the studied rinds which were in the order of 10 8 m a for both basalt and sandstone cobbles these rates are 1 2 orders of magnitude slower than those reported for tropical areas elsewhere most probably due to the lower rainfall in the studied area

basalt weathering across scales abstract weathering of silicate minerals impacts many geological and ecological processes for example the weathering of basalt contributes significantly to consumption of atmospheric carbon dioxide co2 and must be included in global calculations of such consumption over geological timeframes here we compare weathering advance rates for basalt wd where d and indicate the scale at which the rate is determined and surface area measured respectively from the laboratory to the watershed scales data collected at the laboratory weathering rind soil profile and watershed scales show that weathering advance rate of basalt is a fractal property that can be described by a fractal dimension dr 2 3 by combining the fractal description of rates with an arrhenius relationship for basalt weathering we derive the following equation to predict weathering advance rates at any spatial scale from weathering advance rates measured at the bet scale w d k 0 a d r 2 e e a r t here k0 is the pre exponential factor 1 29 107 mm3 mm 2 yr 1 ea is the activation energy 70 kj mol 1 and a is a spatial constant related to the scale of measurement of bet surface area 10 7 mm the term a d r 2 is the roughness the roughness fractal dimension can be conceptualized as a factor related to both the thickness of the reaction front and the specific surface area within the reaction front however the above equation can also be written in terms of a surface fractal dimension and the hypothetical average grain radius these fractal dimensions provide insight into reaction front geometry and should vary with lithology once the surface area discrepancy has been accounted for using this method we find a one to two order of magnitude range in weathering advance rates measured at any scale or temperature that can be attributed to factors such as changes in erosional regime parent lithology mechanism climate composition of reacting fluid and biological activity our scaled equation when used to predict global basalt co2 consumption based upon global lithologic maps yields an uptake flux 1 75 1013 mol co2 yr 1 within the predicted error of fluxes estimated based upon riverine measurements

geomorphological investigations and luminescence dating in the southern part of the khangay and the valley of the gobi lakes central mongolia geomorphological investigations in the catchment area of the baydragiyn river along the southern slope of the khangay and in the valley of the gobi lakes in western mongolia provide evidence for late quaternary glaciations and lake level changes thermoluminescence tl and infrared optically stimulated luminescence irsl dating of aeolian and colluvial sediments from the central khangay place the sediments that overlie fluvial and glaciofluvial terraces in the holocene an age of 21 ka is determined for a sand deposit overlying the terrace that is related to the last glacial ice margin lacustrine sediments from higher beach lines in the valley of the gobi lakes provide evidence for a slightly more humid period around 1 5 ka and a larger extent of the lakes in the early holocene at about 8 5 ka as also reported from other parts of central asia remnants of lacustrine sediments buried by alluvial gravel and indicating a huge palaeolake in the basin of the orog nuur however date to the early stage of the last glaciation around 70 ka copyright 2001 john wiley sons ltd

uplift age and rates of the gurvan bogd system gobi altay by apatite fission track analysis abstract the dating of the uplift onset of the mongolian mountain ranges the northernmost relief associated with the india eurasia convergence is a fundamental issue to better understand the mechanisms of propagation of the cenozoic transpressive deformation in central asia using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the gurvan bogd system in the gobi altay since the middle mesozoic to the late cenozoic the region was firstly affected by a lower middle jurassic tectonic phase characterized by a vertical crustal movement larger than 2 km then followed a protracted period without major crustal vertical movements until the last uplift phase the peneplanation of the jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 ma this same surface corresponds to the present summit plateaux of the massifs standing about 2000 m above the surrounding region which corresponds to the vertical movement produced by the ongoing uplift modelling of fission track data from the massifs of ih bogd and baga bogd shows that this uplift phase probably started at 5 3 ma the gobi altay mountain range appears therefore as one of the youngest mountain ranges in central asia which is consistent with the idea of a northward propagation of the transpressional deformation from the himalayan front to the siberian craton the cenozoic uplift rate of the massifs is estimated to be between 0 25 and 1 mm yr which is slightly higher than the upper pleistocene vertical slip rates of the bordering faults this suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries

sedimentary processes vertical stratification sequences and geomorphology of the roaring river alluvial fan rocky mountain national park colorado abstract the roaring river alluvial fan formed on 15 july 1982 in rocky mountain national park colorado by a catastrophic flood that was generated by a dam failure the fan covers an area of 0 25 square km has a radial length of 0 7 km and is up to 14 m thick sedimentation occurred in three phases each producing a distinct fan lobe initial sedimentation was by a noncohesive sediment gravity flow which deposited two levees on the proximal boundaries of lobe i the levees consist of a poorly sorted mixture of logs sand pebbles cobbles and boulders the first two lobes were built primarily by sheetflooding which deposited imbricated boulders in trains behind obstacles that formed as jams between boulders or logs and upright trees horizontally laminated granule and sand sedimentation took place down fan from the boulders due to deceleration of the expanding sheetflood thin to medium interbedded sand and cobble pebble gravel couplets were deposited by sheetflooding on the third lobe gravel was transported as bedload by supercritical flow and deposited locally where antidunes broke sand was transported as suspended load and deposited where flood velocity locally decreased due to destruction of antidunes increased roughness or flow separation around the low amplitude gravel bed forms the flood rechannelized at the distal end of lobe iii due to constriction between the fan and the valley margin deposits in the upper rechannelized reaches consist of crudely bedded cobble and pebble gravel and interstratified pebble gravel and backset bedded sand deposition was by supercritical flow in the lower reaches planar cross bedded sandy pebble gravel and climbing ripple horizontal trough cross bedded and backset bedded sand were deposited by supercritical and subcritical flow the flood deposit was modified during waning flood stage and during the three years following the flood by noncatastrophic discharge events these events formed braided distributary channels by erosion into the top of the sheet flood deposits fan building took place mostly by catastrophic unconfined discharge whereas much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge

slip rate and slip magnitudes of past earthquakes along the bogd left lateral strike slip fault mongolia we carried out morphotectonic studies along the left lateral strike slip bogd fault the principal structure involved in the gobi altay earthquake of 1957 december 4 published magnitudes range from 7 8 to 8 3 the bogd fault is 260 km long and can be subdivided into five main geometric segments based on variation in strike direction west to east these segments are respectively the west ih bogd wib the north ih bogd nib the west ih bogd wib the west baga bogd wbb and the east baga bogd ebb segments morphological analysis of offset streams ridges and alluvial fans particularly well preserved in the arid environment of the gobi region allows evaluation of late quaternary slip rates along the different faults segments in this paper we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the bogd fault our results show that the left lateral slip rate is similar to 1 mm yr 1 along the wib and eib segments and similar to 0 5 mm yr 1 along the nib segment these variations are consistent with the restraining bend geometry of the bogd fault our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the bogd rupture complementing previously published studies we show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5 2 m in the west to 2 0 m in the east reflecting the progressive change of kinematic style from pure left lateral strike slip faulting to left lateral reverse faulting along the three western segments we measure cumulative displacements that are multiples of the 1957 coseismic offset which may be consistent with a characteristic slip moreover using these data we re estimate the moment magnitude of the gobi altay earthquake at m w 7 78 7 95 combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500 5200 yr for past earthquakes along the different segments of the western bogd fault this suggests that the three western segments of the bogd fault and the gurvan bulag thrust fault a reverse fault bounding the southern side of the ih bogd range that ruptured during the 1957 earthquake have similar average recurrence times and therefore may have ruptured together in previous earthquakes as they did in 1957 these results suggest that the western part of the bogd fault system including the gurvan bulag thrust fault usually behaves in a characteristic earthquake mode

cenozoic normal faulting and regional doming in the southern hangay region central mongolia implications for the origin of the baikal rift province abstract the hangay dome in central mongolia is a mountainous region covering more than 200 000 km2 with numerous flat topped peaks over 3000 m that preserve a late cretaceous paleogene erosion surface doming began in the middle oligocene producing more than 2000 m of regional topographic uplift the range represents an important kinematic link between the baikal rift province to the north and altai transpressional ranges to the south and west structural field investigations of major faults visible on satellite imagery indicate that the southern hangay dome region is dominated by late cenozoic normal faults that bound small half graben most faults are ne striking and faults at the highest elevations are the most recently active most graben appear to be isolated systems that constitute small sediment sinks perched on the flanks and crests of the dome the first order feature is the dome itself and most sediment eroded off of the dome is deposited in the mongolian valley of lakes or is carried northwards by the selenga river and its extensive tributaries the basement of the dome is a precambrian craton although the shape and dimensions of the craton are poorly constrained to the north and east late cenozoic uplift of the southern dome region appears to be confined to the area underlain by cratonic basement whereas the altai region to the south and west is underlain by mechanically weaker palaeozoic arc and accretionary belts with respect to the regional northeast directed shmax the hangay craton appears to have acted as a rigid passive indentor focusing late cenozoic transpressional deformation around its west and southern margins models invoking a late cenozoic plume as the driving force for doming and widespread alkaline volcanism on the dome are not strongly supported by geochemical and isotopic data on neogene recent volcanics and the spatial correlation between areas that are domed and older cratonic crust appears too coincidental to be ignored convective removal of an overthickened lithospheric root leading to adiabatically decompressed asthenosphere could explain regional doming and volcanism however major crustal thickening last occurred in the permian in the southern hangay region and the time lag between thickening and postulated root removal and plateau uplift 200 myr appears too long an alternative model is explored based on speculated lithospheric mantle flow patterns driven by india s continued northeastward indentation it is suggested that lithospheric mantle flow diversion around the overthickened hangay craton crustal keel could cause lithospheric thinning beneath the craton and passive asthenospheric upwarp leading to regional topographic uplift and decompression melting alkali volcanism in general the angular relationship between precambrian craton boundaries and the prevailing northeasterly shmax appears to control the kinematics of late cenozoic deformation throughout the hangay altai sayan and baikal regions

controls on modern fan morphology in calabria southern italy abstract alluvial fans are widespread throughout calabria but only a minority display evidence of current activity in order to understand if and to what extent fan types and their morphology are dependent on the physical environment including characteristics and processes of the depositional site and drainage basin we performed a series of discriminant analyses these analyses used as classification factors the presence or absence of fill in the feeder channel conditions of confinement by host terrain the dominant depositional process debris flow or sheetflood and morphometric attributes of fans and drainage basins as the discriminant function variables in general fan slope area and width length ratio and for basins melton s ruggedness number and source ratio were the most useful variables for classification best results were obtained by discriminating the types of fan deposits and the presence versus absence of fill in the feeder channel if the feeder source is singular fan morphology is controlled by constructional processes and is tightly linked to basin morphology on the other hand fan and basin morphology are also strongly dependent on the rock mechanical characteristics with hard rocks imparting to the basin a high ruggedness and to fans a high gradient larger fans however are those where sheetflooding predominates results of discriminant analysis based on fan and basin variables are much more significant than those based on fan variables only this means that the differences between characteristics of fan and basin systems are better defined than those between characteristics of fans only

chemical weathering in the foreland of a retreating glacier chemical denudation rates and strontium isotope ratios in streams vary substantially and systematically in the foreland of the retreating bench glacier in south central alaska to study weathering of young glacier sediments we sampled 12 streams draining a chronosequence of till and moraine soils derived from cretaceous metagraywacke metapelite bedrock both sediment age and vegetation cover increase with distance from the glacier cation denudation rates decline with increasing distance from the glacier whereas silica denudation rates increase carbonate dissolution and sulfide oxidation account for roughly 90 of the solute flux from the youngest sediments biotite alteration accounts for 5 11 of the solute flux its peak contribution is found in the glacier outlet stream silicate weathering is the dominant reaction only in the oldest sediments in a laboratory dissolution experiment using fresh glacial sediment carbonate dissolution dominated the solute flux during the first 700 hours paralleling the behavior of young sediments in the field in contrast to trends in the field the silica flux did not increase after the carbonate was exhausted from the reactor a possible reason for this difference is that establishment of vegetation causes an increase in silicate weathering the 87sr 86sr ratio in the glacier outlet stream is greater than that in proglacial streams and in bulk rock due to a greater contribution of biotite weathering in the outlet than in proglacial streams strontium isotope ratios decline with sediment exposure age in the proglacial streams and are consistent with a carbonate source because the dominant weathering reactions in the young sediments are of carbonate and sulfide rather than silicate minerals weathering at the glacier margin is not an important long term sink for atmospheric co2

chemical weathering and associated co2 consumption in the mahanadi river basin india abstract chemical weathering of continents is one of the major geochemical processes which consumes atmospheric co2 and exerts a strong impact on the global climate the major ion chemistry of the mahanadi river basin one of the largest river basins in india is determined to investigate the sources of major ions and their spatio temporal variability chemical weathering rates and associated co2 consumption in the basin the results reveal that the ions in the basin are dominated by ca and hco3 the total dissolved solids 215 mg l 1 in monsoon and 270 mg l 1 in pre monsoon and total cation concentration 2367 eq in monsoon and 3214 eq in pre monsoon in the basin are relatively higher than the global average the dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates the estimated chemical weathering rates based on the forward model are 44 94 t km 2 yr 1 in monsoon and 2 45 t km 2 yr 1 in pre monsoon with annual average chemical weathering rate of 23 7 t km 2 yr 1 the contribution of silicate weathering rates in the basin is 32 and 1 55 t km 2 y 1 during monsoon and pre monsoon period respectively the estimated co2 consumption rate associated with chemical weathering in the basin is 13 3 105 mol km 2 yr 1 during monsoon and 0 66 105 mol km 2 yr 1 during pre monsoon period with an average annual rate of 6 9 105 mol km 2 yr 1 which is higher than the global average the net rate of co2 consumption by silicate weathering is estimated to be approximately 4 78 105 mol km 2 yr 1 it is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin however the basin elevation has a good negative correlation with chemical weathering rate

sedimentary processes and facies of the waterlaid anvil spring canyon alluvial fan death valley california the anvil spring canyon fan of the panamint range piedmont in central death valley was built entirely by water flow processes as revealed by an analysis of widespread 2 to 12 m high stratigraphic cuts spanning the 9 7 km radial length of this 2 5 5 0 sloping fan two facies deposited from fan sheetfloods dominate the fan from apex to toe the main one 60 95 of cuts consists of sandy granular fine to medium pebble gravel that regularly and sharply alternates with cobbly coarse to very coarse pebble gravel in planar couplets 5 25 cm thick oriented parallel to the fan surface the other facies 0 25 of cuts comprises 10 to 60 cm thick wedge planar and wedge trough beds of pebbly sand and sandy pebble gravel in backsets sloping 3 28 both facies are interpreted as resulting from rare sediment charged flash floods from the catchment and were deposited by supercritical standing waves of expanding sheetfloods on the fan standing waves were repeatedly initiated enlarged migrated and then terminated either by gradually rejoining the flood or by more violent breakage and washout the frequent autocyclic growth and destruction of standing waves during an individual sheetflood resulted in the deposition of multiple coarse and fine couplet and backset sequences 50 250 cm thick across the active depositional lobe of the fan erosional intensity during washout of the standing wave determined whether early phase backset bed deposits or washout phase sheetflood couplet deposits were selectively preserved in a given cycle two minor facies are also found in the anvil fan pebble cobble gravel lags 0 20 of cuts are present above erosional scours into the sheetflood couplet and backset deposits they consist of coarse gravel concentrated through fine fraction winnowing of the host sheetflood facies by sediment deficient water flows this reworking occurred during recessional flood stage or from non catastrophic discharge during the long intervals between major flash floods this facies is common at the surface giving rise to a braided stream appearance however it is stratigraphically limited present as thin continuous to discontinuous beds or lenses that bound 50 to 250 cm thick sheetflood sequences the other minor facies of the anvil fan consists of clast supported and imbricated thickly stratified pebbly cobbly boulder gravel present in narrow radially aligned ribbons nested within sheetflood deposits this facies is interpreted as representing deposition in the incised channel of the fan a subenvironment characterized by greater flow competence resulting from maintained depth from channel wall confinement and by more frequent water flows and winnowing events caused by its direct connection with the catchment feeder channel

forebergs flower structures and the development of large intra continental strike slip faults the gurvan bogd fault system in mongolia the gurvan bogd mountains of the gobi altay mongolia contain a system of strike slip faults with a reverse component part of which moved in a large earthquake mw 8 0 in 1957 adjacent and sub parallel to the main ranges are numerous thrust related folds thrust faults and elongated low ridges forebergs all of which result from the shortening component on the fault zone the appearance of these thrust related structures is varied depending on their stage of development preservation and exposure evidence from geomorphology and surface ruptures suggests that they may all serve a common function which is to broaden the deforming zone by creating new structures that are able to accommodate both the strike slip and the shortening components of motion the geomorphology further suggests that these new structures then evolve by lateral propagation and increase in amplitude to eventually merge and form through going new faults subparallel to the old in their early stages the new faults and related structures appear to be influenced by the underlying sediments adjacent to the main range which may include weak layers such as lake beds that can ultimately cause the collapse of foreberg ridges in landslides the migration of faulting away from the main range is likely to be driven by stresses associated with topography which in turn is a consequence of the shortening component the evolution described here is thus peculiar to strike slip faults with a reverse component and can form many of the features of the flower structures that are often described in such oblique shortening zones although the shortening component is often localized in restraining bends its origin may ultimately be related to rotations about vertical axes which are common in deforming continental regions

quantifying chemical weathering rates along a precipitation gradient on basse terre island french guadeloupe new insight from u series isotopes in weathering rinds abstract inside soil and saprolite rock fragments can form weathering clasts alteration rinds surrounding an unweathered core and these weathering rinds provide an excellent field system for investigating the initiation of weathering and long term weathering rates recently uranium series u series disequilibria have shown great potential for determining rind formation rates and quantifying factors controlling weathering advance rates in weathering rinds to further investigate whether the u series isotope technique can document differences in long term weathering rates as a function of precipitation we conducted a new weathering rind study on tropical volcanic basse terre island in the lesser antilles archipelago in this study for the first time we characterized weathering reactions and quantified weathering advance rates in multiple weathering rinds across a steep precipitation gradient electron microprobe emp point measurements bulk major element contents and u series isotope compositions were determined in two weathering clasts from the deshaies watershed with mean annual precipitation map 1800 mm and temperature mat 23 c on these clasts five core rind transects were measured for locations with different curvature high medium and low of the rind core boundary results reveal that during rind formation the fraction of elemental loss decreases in the order ca na k mg si al zr ti fe such observations are consistent with the sequence of reactions after the initiation of weathering specifically glass matrix and primary minerals plagioclase pyroxene weather to produce fe oxyhydroxides gibbsite and minor kaolinite uranium shows addition profiles in the rind due to the infiltration of u containing soil pore water into the rind as dissolved u phases u is then incorporated into the rind as fe al oxides precipitate such processes lead to significant u series isotope disequilibria in the rinds this is the first time that multiple weathering clasts from the same watershed were analyzed for u series isotope disequlibrian and show consistent results the u series disequilibria allowed for the determination of rind formation ages and weathering advance rates with a u series mass balance model the weathering advance rates generally decreased with decreasing curvature 0 17 0 10 mm kyr for high curvature 0 12 0 05 mm kyr for medium curvature and 0 11 0 04 0 08 0 03 0 06 0 03 mm kyr for low curvature locations the observed positive correlation between the curvature and the weathering rates is well supported by predictions of weathering models i e that the curvature of the rind core boundary controls the porosity creation and weathering advance rates at the clast scale at the watershed scale the new weathering advance rates derived on the low curvature transects for the relatively dry deshaies watershed average rate of 0 08 mm kyr map 1800 mm and mat 23 c are 60 slower than the rind formation rates previously determined in the much wetter bras david watershed 0 18 mm kyr low curvature transect map 3400 mm and mat 23 c also on basse terre island thus a doubling of map roughly correlates with a doubling of weathering advance rate the new rind study highlights the effect of precipitation on weathering rates over a time scale of 100 kyr weathering rinds are thus a suitable system for investigating long term chemical weathering across environmental gradients complementing short term riverine solute fluxes

quantifying the impact of freshwater diatom productivity on silicon isotopes and silicon fluxes lake myvatn iceland diatom productivity in the oceans plays a crucial role in the carbon cycle but is strongly dependent upon the continental silicon supply however the relative influence of weathering and biological processes on continental si fluxes remains poorly constrained this study aims to quantify the impact of terrestrial diatom productivity on si fluxes to the ocean lake myvatn in north iceland is one of the most productive lakes in the northern hemisphere with nutrient rich waters almost uniquely sourced by groundwater the primary production is mainly controlled by diatom growth but also by cyanobacteria and the lake output is via a single river thereby providing a relatively simple natural laboratory to quantify the impact of diatom growth on the chemistry and si budget of lake waters silicon stable isotopes o 30si provide a tracer of this biocycling and have been measured in groundwater inputs to the lake and in time series monitoring of waters at the lake outlet the o 30si values at the outlet range from 0 70 0 08 to 1 42 0 06 which is significantly heavier than the groundwater input average cold and hot springs 0 50 0 17 2sd and consistent with the preferential uptake of light si isotopes by diatoms the o 30si value at the outlet increases by up to 0 9 in spring and autumn relative to the si isotope composition of the inflow these seasonal diatom blooms can be modeled by an open system of si uptake and affect si fluxes at the outlet of the lake by up to 79 or 53 integrated over the year in the summer a shift to lighter o 30si values is correlated with a higher ph which results in dissolution of diatoms releasing light si isotopes from mass balance this seasonal diatom dissolution affects si fluxes by up to 33 but is limited to 3 7 integrated over the year these results clearly illustrate that biological activity can have a significant impact on both isotope composition and elemental abundance of continental derived si they also demonstrate the ph dependency of diatom dissolution and or preservation which is likely to affect not only the continental si fluxes to the ocean but also the si recycling in the oceans themselves

visualization of tectonic structures in shallow depth high resolution ground penetrating radar gpr profiles ground penetrating radar gpr is applied to detect subsurface tectonic structures and to map the geometry of faulted blocks tectonic interpretations from a profile crossing the graben fault and a grid in a second order graben structure providing a 3d data set are correlated to the structural inventory of the outcrop folded layers of the roll over anticline are identified by continuous curved reflectors and an increasing dip towards the main graben fault faults are indicated by arrays of reflector terminations variations in the water and clay content caused by karstification and brecciation on fault planes are displayed by changing amplitudes of the detected signal the 3d visualization of the second order graben structure with a grid of gpr profiles illustrates the local stress pattern which coincides with structural observations in the outcrop and photo lineations

predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first order controls silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways first by the uptake of atmospheric soil co2 and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica dsi previous work suggests that regions dominated by volcanics are hyperactive or even hot spots concerning dsi mobilization here we present a new approach for predicting dsi fluxes to coastal zones emphasizing first order controlling factors lithology runoff relief land cover and temperature this approach is applied to the japanese archipelago a region characterized by a high percentage of volcanics 29 1 of surface area the presented dsi flux model is based on data of 516 catchments covering approximately 56 7 of the area of the japanese archipelago the spatial distribution of lithology one of the most important first order controls is taken from a new high resolution map of japan results show that the japanese archipelago is a hyperactive region with a dsi yield 6 6 times higher than the world average of 3 3 t sio2 km 2 a 1 but with large regional variations approximately 10 of its area exceeds 10 times the world average dsi yield slope constitutes another important controlling factor on dsi fluxes besides lithology and runoff and can exceed the influence of runoff on dsi yields even though the monitored area on the japanese archipelago stretches from about 31 to 46 n temperature is not identified as a significant first order model variable this may be due to the fact that slope runoff and lithology are correlated with temperature due to regional settings of the archipelago and temperature information is substituted to a certain extent by these factors land cover data also do not improve the prediction model this may partly be attributed to misinterpreted land cover information from satellite images implications of results for earth system and global carbon cycle modeling are discussed

tectonics from fluvial topography using formal linear inversion theory and applications to the inyo mountains california tectonic activity generates topography and the variability of tectonic forcing is responsible for topographic patterns and variability of relief in fluvial landscapes despite this basic relation the inverse problem by which features of the topography are used for inferring tectonic uplift rates has proven challenging here we develop formal linear inversion schemes to infer a record of the rate of relative uplift as a function of space and time from the long profiles of rivers the relative uplift rate is the difference between the rates of rock uplift and of the base level change the inversion schemes are based on a closed form analytic solution to the transient linear stream power model and to increase model resolution they make use of the multiplicity of information made available by multiple rivers and their tributaries the distribution of the fluvial response time to tectonic perturbations is a key component of the inversion scheme as this determines which tectonic events are preserved in the topography we develop two inversion parameterizations that differ in their assumptions about the tectonic forcing space invariant and time space variability with an assumed spatial distribution the inversion schemes are applied to the inyo mountains an uplifted block along the western boundary of the basin and range province in california inversion results indicate that the range has been experiencing an acceleration of the relative uplift in the past 2 3 ma we use the inversion results to constrain the paleotopography and paleo erosion rate along the range and to recover the throw rate history along the fault that bounds the inyo range

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

schmidt hammer exposure age dating shd of late quaternary fluvial terraces in new zealand schmidt hammer sh r values are reported for surface clasts from numerically dated holocene and pleistocene fluvial terraces in the south island of new zealand the r values are combined with previously obtained weathering rind radiocarbon terrestrial cosmogenic nuclide and luminescence terrace ages to derive sh r value chronofunctions for greywacke clasts from four distinct locations our results show that different weathering rates affect the form of the sh r value versus age curve however a fundamental dependency between the two remains constant over timescales ranging from 102 to 105 years power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic precipitation and temperature and sedimentologic variables source terrane petrology age uncertainties of 22 of the surface age suggest that schmidt hammer exposure age dating shd is a reliable calibrated age dating technique for fluvial terraces copyright 2013 john wiley sons ltd

uranium thorium chronometry of weathering rinds rock alteration rate and paleo isotopic record of weathering fluids abstract the potential of 238u 234u 230th chronometry for constraining the formation rate of weathering rinds developed on fresh rocks is assessed by analyzing a weathering rind on a basaltic clast from a 125 kyr old costa rican alluvial terrace eighteen subsamples were collected from one section of the clast by drilling cores 4 mm in diameter and 5 mm depth along two transects straddling the core rind boundary variations of major and trace element concentrations along the two transects point out a intense loss of alkaline and alkaline earth elements b conservative behaviour of elements such as zr hf and th and c external input of u into the rind without any evidence of u loss during basalt weathering in addition variations in u concentrations along the transects show that the main u th fractionation process associated with the weathering of the basaltic clast is an external input of u without addition nor loss of th in the basalt rind transition zone and that once deposited u is immobile in the weathering rind in the frame of this interpretation scheme a weathering rate of 0 5 0 2 mm kyr can be calculated for the studied clast which is consistent with geological and isotopic evidence constraining the depositional ages of the terraces in addition the variations in the 234u 238u ratio along the analysed transects as well as the increase in sr isotopic ratios within the weathering rind are best explained by temporal variation of the u activity ratios and sr isotope ratios of the soil solutions brought into the rind this work highlights how well detailed u th chronological studies of weathering rinds can 1 constrain the formation rates of weathering systems and 2 record the time variation of isotopic composition of weathering fluids

morphotectonics of the northern bogd fault and implications for middle pleistocene to modern uplift rates in southern mongolia abstract assessing the activity of strike slip faults is often facilitated by cumulative offsets of morphological features the december 4th 1957 mongolia earthquake generally referred to as the gobi altai or bogd earthquake had mw 8 1 and created long and complex surface ruptures of c 350 km length along the bogd fault that cuts across the foothills of the gurvan bogd mountains several left laterally and vertically displaced quaternary alluvial fans and morphogenic markers show cumulative offsets allowing for an assessment of the effect of repeated earthquakes and active tectonics on landscape evolution we propose to expand the active tectonic record along this fault up to a middle pleistocene time scale that spans regional climatic fluctuations i e repeated glacial interglacial cycles and hence varying erosional and depositional rates five main drainage areas crosscutting the north ikh bogd segment of the bogd fault were analysed and compared in terms of hypsometry drainage steepness and alluvial fan slope inclination along the mountain front deposits from all drainages form multiple alluvial fan levels that reflect recurring deposition incision cycles previously published ages as well as the spatial distribution of these fan levels suggest that their incision and abandonment is induced by regionally dominant climate fluctuations however the increase of fan slope angles over time and the increased intensity of sub surface folding observed in ground penetrating radar profiles suggests that cumulative tectonic uplift also has a strong impact on alluvial fan morphology estimates of the increase of fan slope angles as a result of cumulative tectonic uplift imply that middle pleistocene to modern vertical slip rates along the north ikh bogd segment of the bogd fault are in the order of 0 9 1 mm yr however much slower vertical slip rates along individual fault segments ranging between 0 06 0 01 mm yr and 0 28 0 07 mm yr indicate that uplift of the ikh bogd plateau occurs as a result of distributed deformation across multiple parallel fault strands within bedrock as well as alluvial fans our results emphasise the importance of regional studies along active faults that take into account the complexity of surface ruptures as well as the occurrence of related structures that can accommodate deformation