chemical and physical denudation in the amazon river basin we present major and trace element data on the suspended and dissolved phases of the amazon river and its main tributaries the sr isotopic composition of the dissolved load is also reported special attention is paid to the abundances of ree and to their fractionation between the dissolved and suspended phase the rivers of the amazon basin are among the richest in dissolved ree and are similar to the rivers of the congo system however a greater range of fractionation between lree and hree is reported here at a global scale the rivers have intermediate patterns between those of the congo system and those of high ph rivers such as the indus and mississippi rivers only few elements rb u ba k na sr and ca are mobilized by silicate weathering these elements are strongly depleted in the suspended phase with respect to upper continental crust in the dissolved load these elements are controlled by atmospheric inputs and the weathering of the main lithologies we propose a model based on mass budget equations that allow the proportions derived from the different sources to be calculated as a consequence silicate carbonate and evaporite weathering rates can be estimated as well as the consumption of co2 by weathering of each of these lithologies physical weathering rates can be estimated by two complementary approaches on the one hand the multi year average of suspended sediments yields can be used to estimate physical denudation on the other hand we have developed a steady state model of erosion that allows us to calculate physical erosion rates on the basis of the dissolved load of rivers a mean crustal composition is assumed in this model for the rock sources of the drainage basins comparison of the rates predicted by the model to the observed rates shows good agreement for the lowland rivers but a strong discrepancy for the rivers derived from the andes andean rivers solimoes madeira and amazon have observed sediment yields much greater than those predicted according to the steady state model of chemical and physical weathering two interpretations can account for this inconsistency the first is that these rivers are not in steady state and hence that the soils are being destroyed the second requires that the local continental crust is different from the average continental crust of taylor and mclennan and contains a large proportion of sedimentary rocks using the measured sediment yields and assuming a steady state we can estimate the amount of sediment recycling for each drainage basin for the amazon at santarem we find that at least 25 of the mass of the upper continental crust of the amazon drainage basin is constituted of recycled material

the nilgiri enderbites south india nature and age constraints on protolith formation high grade metamorphism and cooling history abstract the trident shaped nilgiri highland massif represents the deepest level exposure 9 10 kbar c 35 km palaeo depth of granulite grade lower crust in southern peninsular india the crustal section is essentially composed of garnetiferous enderbitic granulites with minor kyanite bearing gneisses quartzites and banded magnetite quartzites its deeper northern part is intruded by intermediate and basic magmatic rocks now represented by non garnetiferous enderbites garnetiferous basic granulites gabbroic to anorthositic two pyroxene granulites and pyroxenites the garnetiferous enderbitic granulites are tonalitic in composition displaying a typical calc alkaline trend and exhibit chemical features of both i type as well as s type granitoids they show moderate enrichment of lree la n 35 70 no to weakly negative eu anomalies and fairly constant levels of hree yb n 6 5 13 0 and resemble the ree spectra of tonalitic trondhjemitic granitoids and greywackes of late archaean to palaeoproterozoic age sedimentary protoliths are indicated by negative df values ranging from 1 to 4 al 2 o 3 cao na 2 o k 2 o molar ratios 1 1 high 18 o whole rock values 10 12 which match the values reported for greywackes whole rock isotope data for garnetiferous enderbites define linear arrays in the rb sr and sm nd evolution diagrams rb sr system 2460 81 ma with sr i 0 7030 5 sm nd system 2506 70 ma with nd i 0 509363 60 implying a provenance of the sedimentary precursors that was dominated by felsic volcanic rocks or tonalitic trondhjemitic granitoids of uniform isotopic composition and early proterozoic age the u pb systematics of composite zircon grains with detrital cores and metamorphic overgrowths in accord with the sm nd and rb sr errorchron ages and sm nd garnet whole rock data suggest that formation of the provenance deposition of the sedimentary precursors and subsequent high grade tectono metamorphic processes must have occurred in the short time span between 2600 and 2500 ma based on the regional geological framework the petrological geochemical and isotopic data the nilgiri granulite terrain is interpreted as a metasedimentary allochthonous unit that was thrust onto the dharwar craton during palaeoproterozoic collisional tectonics

major and trace element abundances and strontium isotopes in the nyong basin rivers cameroon constraints on chemical weathering processes and elements transport mechanisms in humid tropical environments this paper aims to improve our understanding of chemical weathering processes and element transport mechanisms in the humid tropical environments we studied the nyong river basin 27 800 km2 located on the northwestern part ntem complex of the congo craton central africa the dissolved concentrations i e 0 20 m of major and trace elements dissolved organic carbon doc and the 87sr 86sr ratios have been measured in more than 20 rivers draining watersheds with various surface areas 1 to 28 000 km2 all these rivers exhibit low major cations concentrations i e na mg k ca but high concentrations of some trace elements al fe th zr y ree silica and doc the total dissolved load tds is low 20 mg l 1 and dominated by silica and organic matter the comparison of different watersheds shows us that chemical weathering is more efficient in the small unit watersheds all the sampled rivers exhibit a wide range of 87sr 86sr ratios and high ca na ratio that can be explained by the heterogeneity of the crystalline rock constituting the cratonic basement four selected rivers mengong awout soo and nyong having different drainage areas and hydrological parameters were sampled over a 2 year period collected data show that all these rivers present the same monthly seasonal variations with higher concentrations during rainy season and lower concentrations during dry season this implies that the weathering and transport mechanisms of small watersheds can be extended to the whole nyong basin in the small unit watersheds chemical weathering mainly occurs in swamp zones where mineral dissolution is enhanced by humic substances these swamp zones constitute a pool of organic rich water which can be quickly mobilized during rain seasons in these waters doc and insoluble element concentrations e g al fe and th were strongly correlated which show the key role of organic colloidal matter in the transport of some insoluble elements some other relationships al vs fe ree vs al were also examined in order to get information about chemical weathering or element transport based on these data it has been concluded that the chemical composition of these river waters is controlled by geomorphic and historic factors e g thick cation poor soil in contrast the present day climatic parameters high rainfall and temperature play a minor role in water chemistry regulation even though they are likely to enhance mineral dissolution even if organic matter favors mineral dissolution chemical weathering in this area is low compared to other world regions which suggest on a global scale a relatively small effect of these environments on the co2 consumption

rb sr ages of late archean metavolcanics and granites dharwar craton south india and evidence for early proterozoic thermotectonic event s abstract the archean greenstone sequence of the dharwar craton is intruded by late and post kinematic granites like the chitradurga and toranagallu closepet granites with whole rock rb sr isochron ages of 2603 28 ma 2 and 2452 50 ma respectively the whole rock rb sr ages of their host metavolcanic rocks show a wide variation bababudan 2728 102 ma shimoga 2520 62 ma ingaldhal 2240 50 ma mardihalli 2160 174 ma gadag 2456 76 ma and sandur 2377 646 ma while the ages of the bababudan and the shimoga volcanic suites can be related to the time of the pervasive regional folding and metamorphic events 2 7 2 6 ga those of the other volcanic suites from the chitradurga and sandur supracrustal belts indicate effects of post archean thermal event s the internal isochron ages of 2 0 0 1 ga for the chitradurga and toranagallu granites suggest isotopic resetting on a mineral scale about 500 ma after their emplacement and support the evidence from the metavolcanic suites for an early proterozoic thermal event at 2 0 ga in the dharwar greenstone granite gneiss terrain

global methane emission through mud volcanoes and its past and present impact on the earth s climate mud volcanism is an abundant global phenomenon whereby fluid rich low density sediments extrude both on land and offshore methane which generally exceeds 90 vol of the gas phase is emitted at high rates during and after emplacement of the mud domes and is known for its high global warming potential gwp this comprehensive estimate of the annual contribution of mud volcano degassing assesses the significance of mud volcanism for the accumulation of greenhouse gases in the atmosphere a first order estimate for the earlier pre anthropogenic volume of methane released through mud volcanoes further supports their profound effect on the earth s climate since at least the paleozoic 570 ma

anisotropic statistical scaling of vadose zone hydraulic property estimates near maricopa arizona 1 fluid flow and mass transport in the vadose zone are strongly influenced by spatial variability in soil hydraulic properties it has become common to characterize spatial variability geostatistically and to solve corresponding flow and or transport problems stochastically the typical though not only approach is to treat log saturated hydraulic conductivity y log10 ks and perhaps other medium properties as statistically homogeneous isotropic or anisotropic multivariate gaussian random fields with unique variance and autocorrelation scale a growing body of literature suggests that y as well as many other variables may possess heavy tailed non gaussian distributions and or scale dependent statistical parameters representing a multiscale hierarchical structure elsewhere we have demonstrated that these important phenomena are difficult to detect and are not fully tractable with standard geostatistical methods they are however detectable and tractable with a novel geostatistical method of analysis which treats such variables as samples from sub gaussian random fields subordinated to truncated fractional brownian motion tfbm or truncated fractional gaussian noise tfgn each such field is a mixture of gaussian components having random variances the purpose of this paper is to explore the extent to which hydraulic parameters of unsaturated soils exhibit heavy tailed distributions and statistical scaling of the above type as a test bed we have selected an experimental site near maricopa arizona at which soil texture data have been collected in boreholes and trenches to a depth of 15 m over an area of 3600 m2 since hydraulic parameters are difficult to measure to such depths we estimate them using a neural network pedotransfer model input data include percent sand silt and clay outputs include estimates of saturated and residual volumetric water content saturated hydraulic conductivity and due to their wide applicability parameters of the van genuchten mualem constitutive model of unsaturated soil property variations with capillary pressure head we find indeed that vertical and horizontal increments of our hydraulic parameter estimates exhibit heavy tailed frequency distributions and statistical scaling which conform closely to our novel geostatistical framework its generality and applicability to the maricopa site has far reaching implications vis a vis the geostatistical characterization of vadose zone properties and the stochastic modeling of flow and transport in unsaturated media at other sites

genesis of calcic and petrocalcic horizons from coimbatore tamil nadu micromorphology and geochemical studies understanding the development of calcic and petrocalcic horizons is important for palaeoclimate reconstruction the micromorphology and geochemistry of quaternary calcic and petrocalcic horizons formed in the area around coimbatore tamil nadu are discussed the calcic horizons represent the bk horizons that occur as thick complex profiles 300 cm thick in the foothill regions while the laminar petrocalcic horizons representing the k horizon 80 100 cm thick formed on hard rock in the topographic lowlying area calcic horizons are represented by powdery nodular calcrete nodules and root casts with 95 2 64 5 of caco3 laminar petrocalcic horizons are compact with well rounded coalesced nodules and contain 56 64 caco3 micromorphological study of the calcic horizons show the occurrence of alveolar septal structures calcified filaments coated grains spherulites calcified root cells and calcispheres that indicate biogenic origins mainly induced by plant root related microbial activity the calcic nodules within the calcic horizons consist of quartz sand grains cemented by finely crystalline grain coating often glaebular and pore filling micrite this development has taken place in phases of soil formation erosion and reworking the inter relationships between these processes have caused variations in the phases of accretion of soil profiles developed in the foothill region microfabrics of laminar petrocalcic horizons with detritus hosts show replacement corrosion displacement and shrinkage indicating that the laminar petrocalcic horizon formed under relatively semi arid conditions these characteristics indicate that the laminar petrocalcic horizons formed in a moderately near surface environment with relatively high rates of evaporation and ground water action and are polygenetic in origin r 2007 published by elsevier ltd

volcanoes making calderas from mud mud volcanoes often exhibit calderas which are large circular depressions at their summit detailed mapping around the caspian sea suggests that caldera forming mud volcanoes are dynamically similar to magmatic volcanoes

formation and preservation of pedogenic carbonates in south india links with paleo monsoon and pedological conditions clues from sr isotopes u th series and rees the influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the western ghats karnataka plateau south west india has been studied along the climosequence the current mean annual rainfall mar varies within a 80 km transect from 6000 mm at the edge of the plateau to 500 mm inland pedogenic carbonates occur in the mar range of 500 1200 mm in the semi arid zone mar 500 900 mm carbonates occur i as rhick hardpan calcretes on pediment slopes and ii as nodular horizons in polygenic black soils i e vertisols in the sub humid zone mar 900 1500 mm pedogenic carbonates are disseminated in the black soil matrices either as loose irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size they also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate cemented lumps of centimetric to decimetric size chemical and isotopic sr 87 sr 86 compositions of the carbonate fraction were determined after leaching with 0 25 n hcl the corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed the trend defined by the sr 87 sr 86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition considering the residual fraction of each sample as the most likely lithogenic source of ca in carbonates it is estimated that from 24 to 82 55 on average of ca is derived from local bedrock weathering leading to a consumption of an equivalent proportion of atmospheric co2 these values indicate that climatic conditions were humid enough to allow silicate weathering mar at the time of carbonate formation likely ranged from 400 to 700 mm which is 2 to 3 fold less than the current mar at these locations the sr u and mg contents and the u 234 u 238 activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation the relatively high concentrations of sr u and mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite possibly due to a better confinement of the pore waters which is supported by their high u 234 u 238 signatures and or to higher content of dissolved carbonates in the pore waters the occurrence of ce mn and fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation the carbonate ages determined by the u th method range from 1 33 0 84 kyr to 7 5 2 7 kyr and to a cluster of five ages around 20 kyr i e the last glacial maximum period the young occurrences are only located in the black soils which therefore constitute sensitive environments for trapping and retaining atmospheric co2 even on short time scales the maximum age of carbonates depends on their location in the climatic gradient from about 20 kyr for centimetric nodules at mule hole mar 1100 mm yr to 200 kyr for the calcrete at gundlupet mar 700 mm yr durand et al 2007 the intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils c 2010 elsevier ltd all rights reserved

weathering of charnockites and sediment production in the catchment area of the cauvery river southern india abstract in the cauvery catchment area charnockites are making high hills compared to gneisses in situ static weathering of a charnockitic boulder shows lesser extent of chemical weathering relative to that developed into a profile this difference is seen both in clay mineral composition their ree patterns and in the a cn k and a cnk fm triangular plots based on the chemical changes relative to ti three groups of elements are recognized ba si k na sr ca and mg show increasing depletion as the weathering intensity increases in listed order al remained relatively immobile whereas fe followed by mn cr ni ree and p show a variable extent of enrichment with increasing chemical weathering the sediment occurring on the foothills of the charnockite hills have a very uniform composition and texture without any depositional features reworking of these sediments in a first order stream has caused only minor compositional changes by the local segregation of heavy minerals on the channel bed and by the removal of small amount of clay materials as suspended load the ree pattern of the reworked channel bed sand is nearly identical to that of the channel wall sediments but with lower by 25 abundance although the rocks are 2500 ma and now located in tropical latitudes and probably had experienced several periods of warm and wet climate the soils and the sediments derived from them are chemically very immature suggesting their exposure to denudational processes very recently by tectonic uplift

sediment transport in the cauvery river basin sediment characteristics and controlling factors abstract during the monsoon period 75 of the annual rainfall 73 of the annual water discharge and 85 of the annual sediment transport takes place in the cauvery river basin geology and river water discharge are the major natural factors controlling the sediment transport sediment transport in the cauvery river is greatly influenced by the presence of two major dams built across the river an examination of the particle size distribution of the suspended sediments shows that the less than 20 m fraction accounts for nearly 60 of the total sediment transported by the river at dam sites coarse sediments are selectively removed from the suspended load the suspended mineralogy is dominated by quartz and feldspar followed by clay minerals and carbonates clay minerals average about 30 and are dominated by the montmorillonite type the results of our study also demonstrate the importance of such sediment characteristics as particle size and mineralogy in controlling the trace metal distribution in sediments

chemical weathering in the hong red river basin rates of silicate weathering and their controlling factors abstract the hong red river drains the prominent red river fault zone that has experienced various tectonic activities intrusion of magma exhumation of basement rocks and influx of thermal waters associated with the cenozoic collision of india and eurasia we report dissolved major element and sr isotope compositions of 43 samples from its three tributary systems da thao hong main channel and lo encompassing summer and winter seasons carbonic acid ultimately derived from the atmosphere is the main weathering agent and sulfuric acid from pyrite oxidation plays a minor role seasonality is manifested in higher calcite saturation index and mg tz and lower ca mg in summer suggesting calcite precipitation and in higher si na k ratios in summer suggesting more intensive silicate weathering we quantified the input from rain evaporite carbonate and silicate reservoirs using forward and inverse models and examined the robustness of the results carbonate dissolution accounts for a significant fraction of total dissolved cations 55 97 and weathering of silicates makes a minor contribution 1 40 our best estimate of the spatially averaged silicate weathering rate in the hong basin is 170 103 mol km2 yr in summer and 51 103 mol km2 yr in winter we tested for correlations between the rate of co2 consumption by silicate weathering and various climatic air temperature precipitation runoff and potential evapotranspiration and geologic relief elevation slope and lithology parameters calculated using gis clear correlations do not emerge except for co2 and runoff in winter which we attribute to the complex geologic setting of the area the seasonal regime change from physical dominant in summer to chemical dominant in winter and the incoherent timescales involved for the different parameters tested

stochastic analysis of macrodispersion in gravity dominated flow through bimodal heterogeneous unsaturated formations 1 first order analysis based on a stochastic continuum presentation of the flow and a general lagrangian description of the transport was used to investigate the effects of a few characteristics of a bimodal heterogeneous partially saturated formation on the principal components of the time dependent macrodispersion coefficient under steady state unsaturated flow conditions results of the present analysis show that generally a bimodal distribution of the formation properties characterized by a relatively complex spatial correlation structure contributes to the variability in water velocity and consequently may considerably enhance solute spreading this applies especially in formations in which 1 the correlation length scales and the variances of the soil properties associated with the embedded soil are much larger than those of the background soil 2 the contrast between mean properties of the two subdomains is large 3 mean water saturation is relatively small and 4 the volume fraction of the flow domain occupied by the embedded soil is relatively large one of the major findings of this study is the important role played by the formation parameter under unsaturated flow conditions consequently the macrodispersion in a bimodal unsaturated formation may be larger than its counterpart in a saturated formation especially when the degree of saturation decreases when the volume fraction of the flow domain occupied by the embedded soil increases when the disparity between the correlation length scales of the two subdomains is relatively small and when the texture of the embedded soil is coarser than that of the background soil

solute transport through a heterogeneous coupled vadose saturated zone system with temporally random rainfall the transport of nonreactive solutes through a coupled two dimensional randomly heterogeneous vadose saturated zone system subject to temporally random rainfall is predicted by monte carlo simulation and compared with previously published analytic results for three different rainfall patterns the relative contributions of the uncertain inputs i e rainfall and saturated conductivity to the prediction uncertainty of solute transport are quantified in terms of the statistical moments of the pore water velocity the plume spatial moments and solute flux breakthrough curves at downstream control planes results show that the mean and variance of the saturated zone pore water velocity were approximately equivalent for the cases of uniform and random rainfall and were well predicted by the analytical relationships developed by rubin and bellin 1994 as a result the mean plume displacement estimated by the trajectory of the mean plume center of mass was found to be nearly identical for these cases in the temporally random rainfall case the saturated zone mean plume experienced more spread in the direction of mean flow at early times however the asymptotic rates of spatial spreading of the mean solute plumes were found to be approximately equivalent for the uniform and random rainfall cases and well predicted by the approximate expressions for longitudinal macrodispersivity in nonuniform flow proposed by destouni and graham 1995 random rainfall and random soil properties increased prediction uncertainty of the solute plume behavior in the vadose zone by an order of magnitude when compared with the uniform rain and random soil case this effect was reduced considerably when the solute entered the saturated zone where random rainfall produced only slightly larger prediction uncertainty than the uniform rainfall case the analytic model developed by destouni and graham 1995 accurately predicted the temporal breakthrough of the mean solute plume at saturated zone control planes for all cases if transport through the unsaturated zone accounted for the effects of temporally random rainfall using the methodology developed by foussereau et al 2000a 2000b results of this work indicate that for the humid climates studied here uncertain rainfall patterns dominate transport prediction uncertainty in the shallow unsaturated zone while uncertain solute breakthrough to the saturated zone and uncertain hydraulic conductivity dominate prediction uncertainty in the saturated zone

carbon river fluxes and weathering co2 consumption in the congo and amazon river basins data on carbon river fluxes recently obtained by the authors for the congo basin within the framework of the pirat program insu cnrs orstom are compared with results previously obtained for the amazon basin a special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges the flux of atmospheric and soil co2 consumed by rock weathering is estimated to be 3 1 105 and 0 5 105 moles a km2 respectively for the amazon and the congo basin these co2 fluxes represent respectively 67 4 and 74 7 of the total bicarbonate river fluxes a comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas a transfer function between the weathering co2 flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century these interannual co2 fluctuations present average increasing trends of 10 for amazon basin and only 0 7 for the congo basin during the last century

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

macrodispersion in sand shale sequences macrodispersion in sand shale sequences is investigated by a series of numerical tracer tests hydraulic conductivity is modeled as a binary spatially correlated random function realizations of the random conductivity field are simulated on a nodal grid discretizing the heterogeneous formation corresponding realizations of the random velocity field are obtained by solving the equation for saturated steady state flow particle tracking with flux weighted tracer injection and detection is used to generate experimental residence time distributions rtds moments of the rtd are used to characterize longitudinal tracer spreading results show that macrodispersive transport in sand shale sequences cannot be represented by a fickian model rtds display a bimodal structure caused by the fast arrival of particles traveling along preferential sandstone channels and by the much slower arrival of particles following tortuous routes through sandstone and shale the relative importance of channeling and tortuous flow transport mechanisms is determined by sand shale conductivity contrast shale volume fraction and conductivity spatial correlation structure channeling is promoted by high conductivity contrasts low shale fractions and flow parallel to bedding in anisotropic media low contrasts high shale fractions and flow perpendicular to bedding act to break up channels and to enhance tracer spreading

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

geochemistry of femn formations of the archaean sandur schist belt india mixing of clastic and chemical processes at a shallow shelf abstract the late archaean greenstone belts of karnataka are unique in having manganese formations with mineable ores an excellent example of these mn bearing greenstone belts is the sandur schist belt where fe mn formations are confined to the basin shelf clearly separated from the deeper water manganese free bif that accumulated at the basin margin and flanking the marine basin sedimentary textures and structures including stromatolites show that fe mn formations have been deposited on a shallow shelf within the photic zone and above wave base along with quartz fe mn minerals found in arenites argillites and carbonates include ripidolite mg chlorite sericite mn siderite kutnahorite dolomite ferroan dolomite psilomelane pyrolusite cryptomelane haematite and magnetite the manganese and iron contents of these rocks range up to 25 and 46 respectively al 2 o 3 tio 2 mgo cao mno 2 fe 2 o 3 t abundances and ratios show a wide variation ni cr co zr v sc rb sr u th ree lree hree la ce and eu anomalies and their binary relationships indicate that wherever the terrigenous component has increased the concentration of elements of felsic parentage such as zr and hf has gone up elevated concentrations of ni cr co and sc are contributed by chlorite and other components characteristic of basic volcanic debris the carbonates where clastic input is minimal are extremely depleted in ree and other trace elements it is proposed that feo mno and sio 2 probably were added to archaean ocean water at oceanic ridge vents the compositional data suggest that the fe mn formations of the sandur schist belt were generated by chemical and clastic sedimentary processes on a shallow shelf that led into a deeper basin open on one side in this environment chemical and clastic sediments and organic matter were mixed and buried during transgression chemical precipitation took place at the sediment water interface whereas at the time of regression these chemical sediments were buried by clastic sediments redox potential differences between the watermasses on the shallower and deeper shelf respectively fractionated fe and mn the fe mn formations were deposited within the photic zone and above wave base and in a setting where the water column was oxygenated but organic material accumulated by contrast bif was deposited below both wave base and photic zone in a relatively oxygen deficient setting where formation of stable mn oxides was not possible fe mn formation and bif provide an important constraint on greenstone tectonics a shorter distance between archaean oceanic ridge and shelf environments namely the smaller plates model appears to explain several features of fe mn formations bifs and greenstone belts

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

soils and climatic geomorphology on the karnataka plateau peninsular india abstract as a result of extensive field reconnaissance in southern india a geographical traverse across the planation surface of the karnataka uplands which lie in the rainshadow of the western ghats was selected to assess the consequences of a steep rainfall gradient on soil and landform patterns the study of the traverse described in detail reveals a characteristic progression of soil type and wash divide form from the high rainfall to the semi arid end of the continuum and invites a critical reappraisal of classical notions in climatic geomorphology and the soil sciences the assumption that alternations of wet and dry climates are necessary to achieve planation is given special consideration and the often held belief that kaolinite minerals are diagnostic of humid palaeoclimates when found in a semi arid climate is challenged the findings for the indian traverse are set against the better known data for west africa where the rainfall range between the gulf of guinea and the sahel is comparable with that observed in the south western deccan differences outweighing similarities attention is drawn to the possibility that tectonic regime which also controls the degree of landscape stripping is a major key to understanding the climatic geography of soils the tread of planation surfaces and the shape of hillslopes from one region of the tropics to another

major and trace elements of river borne material the congo basin the congo river basin is the second largest drainage basin in the world after the amazon the materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the african continent this paper presents the chemical composition of the different phases carried in the congo rivers and is followed by a companion paper devoted to the modelling of major and trace elements the congo river between bangui and brazzaville as well as its main tributaries including a few organic rich rivers also called black rivers were sampled during the 1989 high water stage the three main phases suspended load dissolved load and bedload were analysed for twenty five major and trace elements concentrations normalized to the upper continental crust show that in each river suspended sediments and dissolved load are chemical complements for the most soluble elements ca na sr k ba rb and u while these elements are enriched in the dissolved loads they are considerably depleted in the corresponding suspended sediments this is consistent with their high mobility during weathering another type of complementarity is observed for zr and hf between suspended sediments and bedload related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads compared to other rivers absolute dissolved concentrations of ca na sr k ba rb and u are remarkably low surprisingly high dissolved concentrations are found in the congo waters for other trace elements e g rees especially in the black rivers on a world scale these concentrations are among the highest measured in rivers and are shown to be ph dependent for a number of dissolved trace elements the dissolved loads are systematically normalized to the suspended loads for each river in order to remove the variations of the element abundances owing to source rock variations normalized diagrams for rees are presented and extended to the other elements they strongly support the argument that the apparent higher solubility of trace elements in the congo waters is due to the presence in the dissolved load of a colloidal phase as a result of 0 2 m filtration an important result is that these colloids are strongly depleted in fe and al with respect to the other elements finally the comparison of the dissolved suspended and sandy transport fluxes of each element in the congo basin rivers shows that although the proportions of for example the rees in the dissolved loads of the majority of the congo basin rivers is close to 10 of the total transport flux up to 80 of the rees are transported by the so called dissolved load in the black rivers

late archaean 2550 2520 ma juvenile magmatism in the eastern dharwar craton southern india constraints from geochronology nd sr isotopes and whole rock geochemistry the results of field geochronologic geochemical and isotopic studies are presented for the granitoids that occur east of the closepet batholith up to the kolar schist belt ksb field data such as common foliation strong shear deformation occasionally leading to mylonitization together with petrographic data including reduction in grain size with corroded borders show characteristics of the syn kinematic emplacement of the granitoids single zircon evaporation ages define a minimum age of 3127 ma for the tonalitic trondhjemitic granodioritic ttg basement and 2552 2534 ma plateau ages for the emplacement of the granitoids which slightly predate 20 30 ma the emplacement of the 2518 ma closepet batholith major and trace element data together with isotopic data suggest at least four magmatic suites from closepet batholith to the east which have independent magmatic evolution histories the observed data are compatible with magma mixing for the closepet batholith melting of ttg and assimilation fractional crystallization processes for bangalore granites either melting of heterogeneous source or different degree of melting of the same source for the granitoids of hoskote kolar and fractional crystallization for the western margin of the ksb isotopic nd sr and geochemical data lree and lil elements suggest highly enriched mantle and ancient ttg crust for the closepet batholith enriched mantle and ttg crust for the bangalore granites c a chondritic mantle source for the granitoids of hoskote kolar and the quartz monzonites of the western margin of the ksb and slightly depleted mantle for granodiorites of the eastern margin of the ksb we interpret all these geochronologic geochemical and isotopic characteristics of granitoids from the closepet batholith to the east up to the ksb in terms of a plume model the centre of the plume would be an enriched hot spot in the mantle that lies below the present exposure level of the closepet batholith melting of such an enriched mantle hot spot produces high temperature magmas closepet that penetrate overlying ancient crust where they strongly interact and induce partial melting of the surrounding crust these magmas cool very slowly as the hot spot maintains high temperatures for a long time thus they appear younger 2518 ma on the contrary to the east the plume induces melting of c a chondritic or slightly depleted mantle that produces relatively colder and less enriched magmas which show less or no interactions with the surrounding crust and cool rapidly and appear slightly older 2552 2534 ma this plume model can also account for late archaean geodynamic evolution including juvenile magmatism heat source for reworking inverse diapirism and granulite metamorphism in the dharwar craton

chemical and strontium oxygen and carbon isotopic compositions of carbonates from the lesser himalaya implications to the strontium isotope composition of the source waters of the ganga ghaghara and the indus rivers samples of precambrian carbonate mostly dolomite outcrops collected across the lesser himalaya have been analysed for their mineralogy chemical composition and isotope ratios of sr o and c to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the ganga ghaghara and the indus their sr concentrations range from 20 to 363 ppm 18opdb 1 4 to 12 8 and mn 11 2036 ppm the petrography of the samples their low sr concentrations and wide range of 18o values are suggestive of their postdepositional alteration the 87sr 86sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0 7064 to 0 8935 and are generally more radiogenic than that of contemporaneous seawater comparison of the 87sr 86sr and sr ca ratios among the carbonates and silicates from the lesser himalaya and the source waters of the ganga ghaghara and the indus shows that the values for the source waters overlap with those of the silicates but are much higher than those in carbonates an upper limit of carbonate sr in the various source waters is calculated to be between 6 and 43 assuming that all the ca in the rivers is of carbonate origin the results show that on the average weathering of the precambrian carbonates is unlikely to be a major contributor to the highly radiogenic strontium isotope composition of these source waters however they can be a dominant supplier of radiogenic sr to some rivers on a regional scale the silicate sr component in some of the source waters of the ganga bhagirathi bhilangna alaknanda and ganga ghaghara kali and sarju and the indus sutlej was calculated from the ca na sr na ratios and strontium isotope compositions of these rivers and the silicate endmember these calculations suggest that 33 89 of sr in the bhagirathi bhilangna alaknanda ganga and sarju rivers is of silicate origin whereas in the kali and the sutlej it is much lower only 8 the remaining sr to all these waters has to be supplied from other sources such as weathering of carbonates and evaporites this study underscores the importance of weathering of silicates carbonates and evaporites in contributing to the sr mass balance and 87sr 86sr of the source waters of the ganga ghaghara and the indus the present day silicate and carbonate sr contributions to the sr budget of the rivers vary considerably but among the major source waters of the ganga silicate sr exerts a more dominant control on their sr abundance and 87sr 86sr

preferential flow in a sandy vadose zone 1 field observation abstract field experiments of water movement in the lower portion of an unsaturated zone i e vadose zone are far more difficult to conduct than those in the root zone thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone recent results from field experiments conducted at the hancock agricultural research station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone by using dye tracing and profile excavation field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the central sand area of wisconsin csaw the results confirmed that preferential flow paths constitute the dominant flow pattern at this location water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport the observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper the mechanism and implications of preferential flow are presented in a companion paper

longitudinal and lateral dispersion in an unsaturated field soil lateral and longitudinal dispersion was quantified in a field soil under water unsaturated conditions the relatively mobile dye tracer brilliant blue fcf was applied as a line source and leached into the soil at two different rates of infiltration 4 and 24 mm d 1 respectively the resulting tracer plume was photographically recorded at vertical soil profiles excavated perpendicularly to the line source after 50 100 and 200 mm of cumulative infiltration an image analysis technique was used to determine two dimensional concentration distributions from the photographs average horizontal and vertical concentration distributions were analyzed using the two dimensional advection dispersipn equation model parameters were fitted to optimize the agreement between measured and modeled averaged concentration profiles in both horizontal as well as vertical directions dispersivities showed a dependency on flow rates and amount of cumulative infiltration but this dependency appeared to be related to the degree of irregularities of observed flow patterns large dispersivities were associated with higher degree of irregularities in the flow patterns and vice versa layer boundaries played a significant role for redirecting flow when flow rates were high and cumulative infiltration was large this study demonstrates 1 that more than just the vertical concentration profiles are needed to define the transport regime under unsaturated conditions and 2 that even subtle layer boundaries affect the lateral mixing regime and exert a marked influence on the transport in the main flow direction

controls on intense silicate weathering in a tropical river southwestern india the silicate weathering rate swr and associated carbon dioxide consumption rate ccr in tropical silicate terrain is assessed through a study of the major ion chemistry in a small west flowing river of peninsular india the nethravati river the specific features of the river basin are high mean annual rainfall and temperature high runoff and a precambrian basement composed of granitic gneiss charnockite and minor metasediments the water samples n 56 were collected from three locations along the nethravati river and from two of its tributaries over a period of twelve months chemical weathering rate cwr for the entire watershed is calculated by applying rainwater correction using river chloride as a tracer chemical weathering rate in the nethravati watershed is estimated to 44 t km 2 y 1 encompassing a swr of 42 t km 2 y 1 and a maximum carbonate contribution of 2 t km 2 y 1 this swr is among the highest reported for granito gneissic terrains the assessed ccr is 2 9 10 5 mol km 2 y 1 the weathering index re calculated from molecular ratios of dissolved cations and silica in the river suggests an intense silicate weathering leading to kaolinite gibbsite precipitation in the weathering covers the intense swr and ccr could be due to the combination of high runoff and temperature along with the thickness and nature of the weathering cover the comparison of silicate weathering fluxes with other watersheds reveals that under similar morpho climatic settings basalt weathering would be 2 5 times higher than the granite gneissic rocks c 2012 elsevier b v all rights reserved

geochemistry of the floodplain sediments of the kaveri river southern india abstract the floodplain sediments of the kaveri river southern india derived from archean gneissic and charnockitic source regions show interbedding of silty 4 4 7 and sandy units 1 4 3 7 the geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of nearly 250 km the sandy beds have more variable chemical compositions yet are comparable to those of silty beds except for the diluting effect of quartz silty sediments retain the geochemical signature of prominently exposed source rocks for almost all elements and provide evidence of tectonic instability in the source region the floodplain sediments contain all size grades sand silt and clay which may have resulted in minimizing the biases imposed on suspended and bedload sediments due to sorting the low chemical index of alteration cia the dominance of unweathered primary minerals and the minor proportion of smectitic clay all suggest that the region has been subjected to little chemical weathering this is possible if the region has undergone recent uplift exposing fresh archean rock to surface denudation the formation of fertile farmland along the kaveri river course and its delta is related to these recent geological processes

lithologic and climatologic controls of river chemistry abstract the chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff in all 101 different rivers each draining a primary lithology were examined across the united states puerto rico and iceland to minimize seasonal effects only rivers with at least two years of data were used basaltic catchments were examined in the greatest detail in a survey of hawaiian island watersheds the average river chemistries could be related to the distribution of soil associations within each catchment an analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium ion exchange control on cation ratios among different lithologies unique weathering rate relationships were developed with yields at typical present day runoff rates 1 100 cm y increasing in the order sandstones granites basalts shales and carbonates the bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering thus a warm wet climate or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal

charnockite genesis across the archaean proterozoic terrane boundary in the south indian granulite terrain constraints from major trace element geochemistry and sr nd isotopic systematics abstract major trace element compositions and sr nd isotopic characteristics of charnockitic gneisses from the southern granulite terrain sgt south india are presented the study region encompasses the central segment of the cauvery shear zone system csz and regions within the madurai block mb immediately south of it designated here as the csz mb and mb domains differences in the compositions and source characteristics between charnockitic rocks of the csz vis a vis those of the csz mb and mb regions are highlighted foremost the charnockites and enderbites of the csz show highly fractionated ree patterns with positive eu anomalies depleted hree y and near chondritic end0 and initial 87sr 86sr at ca 2 5 ga consistent with hydrous partial melting of amphibolitic crust with residual garnet and hornblende for the parental melts by contrast modeled at ca 1 8 ga and 0 8 ga the csz mb and mb charnockitic rocks which show a wider range of ti and p relatively lower degree of hree depletion commonly negative eu anomalies and undepleted y present clear evidence for involvement of archaean crustal components in sources of their magmatic protoliths there is also evidence for significant intracrustal melting processes within a thickened crust at elevated temperatures between 800 and 1000 c implications to the controversial archaean neoproterozoic terrane boundary problem of the sgt are discussed

regolith mass balance inferred from combined mineralogical geochemical and geophysical studies mule hole gneissic watershed south india the aim of this study is to propose a method to assess the long term chemical weathering mass balance for a regolith developed on a heterogeneous silicate substratum at the small experimental watershed scale by adopting a combined approach of geophysics geochemistry and mineralogy we initiated in 2003 a study of the steep climatic gradient and associated geomorphologic features of the edge of the rifted continental passive margin of the karnataka plateau peninsular india in the transition sub humid zone of this climatic gradient we have studied the pristine forested small watershed of mule hole 4 3 km2 mainly developed on gneissic substratum mineralogical geochemical and geophysical investigations were carried out i in characteristic red soil profiles and ii in boreholes up to 60 m deep in order to take into account the effect of the weathering mantle roots in addition 12 electrical resistivity tomography profiles ert with an investigation depth of 30 m were generated at the watershed scale to spatially characterize the information gathered in boreholes and soil profiles the location of the ert profiles is based on a previous electromagnetic survey with an investigation depth of about 6 m the soil cover thickness was inferred from the electromagnetic survey combined with a geological pedological survey taking into account the parent rock heterogeneity the degree of weathering of each of the regolith samples has been defined using both the mineralogical composition and the geochemical indices loss on ignition weathering index of parker chemical index of alteration comparing these indices with electrical resistivity logs it has been found that a value of 400 ohm m delineates clearly the parent rocks and the weathered materials then the 12 inverted ert profiles were constrained with this value after verifying the uncertainty due to the inversion procedure synthetic models based on the field data were used for this purpose the estimated average regolith thickness at the watershed scale is 17 2 m including 15 2 m of saprolite and 2 m of soil cover finally using these estimations of the thicknesses the long term mass balance is calculated for the average gneiss derived saprolite and red soil in the saprolite the open system mass transport function indicates that all the major elements except ca are depleted the chlorite and biotite crystals the chief sources for mg 95 fe 84 mn 86 and k 57 biotite only are the first to undergo weathering and the oligoclase crystals are relatively intact within the saprolite with a loss of only 18 the ca accumulation can be attributed to the precipitation of caco3 from the percolating solution due to the current and or the paleoclimatic conditions overall the most important losses occur for si mg and na with 286 106 mol ha 62 of the total mass loss 67 106 mol ha 15 of the total mass loss and 39 106 mol ha 9 of the total mass loss respectively al fe and k account for 7 4 and 3 of the total mass loss respectively in the red soil profiles the open system mass transport functions point out that all major elements except mn are depleted most of the oligoclase crystals have broken down with a loss of 90 the most important losses occur for si na and mg with 55 106 mol ha 47 of the total mass loss 22 106 mol ha 19 of the total mass loss and 16 106 mol ha 14 of the total mass loss respectively ca al k and fe account for 8 6 4 and 2 of the total mass loss respectively overall these findings confirm the immaturity of the saprolite at the watershed scale the soil profiles are more evolved than saprolite but still contain primary minerals that can further undergo weathering and hence consume atmospheric co2

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

pedogenic carbonates on precambrian silicate rocks in south india origin and paleoclimatic significance abstract calcrete in alfisols on precambrian silicate rocks is studied here in an attempt to reconstruct paleorainfall trends in semiarid south india facies of observed carbonate accumulation are pseudomycelium calcrete nodules nodular horizons hardpan and laminar horizons based on geochemical and sr isotope tracing we relate the presence of calcrete to local geologic conditions within the precambrian basement notably discrete ca rich metamorphic outcrops and rule out eolian input micromorphologic analysis reveals a multi stage origin of the calcretes involving soil colluvial geochemical and biologic processes mostly in vadose environments preliminary u th ages of 190 200 ka obtained on calcrete nodules suggest a major phase of ca release rock weathering and precipitation during marine oxygen isotope stage 7 the calcrete thus indicates fairly stable semiarid conditions at the 200 ky time scale despite fluctuations around an annual rainfall average close to current values 700 mm the stability of the western ghats barrier as a shield to the southwest monsoon explains the long term average stability of the pedoclimatic environment in the rainshadow zone the radiometric ages suggest that weathering may occur massively at discrete intervals of geologic history during spikes of humidity in the paleoclimatic record the rest of the time is spent recycling and redistributing the products of weathering incrementally at landscape scale within seasonal cycles of a relatively stable semi arid climate dating the calcrete therefore does not equate with dating the soil but instead the residence times of nodules in a dynamic soil system in which different constituents have different turnover rates

stochastic analysis of simulated vadose zone solute transport in a vertical cross section of heterogeneous soil during nonsteady water flow the problem of transport of a conservative nonreactive solute in a vertical cross section of a hypothetical partially saturated scale heterogeneous soil under transient water flow was analyzed here it was assumed that locally the water flow and the solute transport can be described by the richards equation and by the one component convection dispersion equation respectively the simulated water content and the solute concentration distributions in the vertical cross section of the soil at different elapsed times were quantified in terms of space averages and two point autocorrelation functions the time evolution of the solute plume was quantified in terms of its first two normalized spatial moments from which the time dependence of the longitudinal and the transverse components of the solute velocity vector and the spatial covariance tensor were estimated the results of this study which are relevant to solute transport at the local or the plume scale demonstrated the considerable variability in the solute concentration in space and time due to the complex heterogeneity of the soil hydraulic properties in both the vertical and the horizontal directions consequently the movement of the solute plume was characterized by a compression expansion phenomenon attributed to the decrease in the effective solute velocity through the zones of relatively fine textured soil material it was concluded that existing stochastic vadose zone transport models may be applicable to shallow depths but may fail to describe the actual spread of a solute plume when the transport takes place at relatively large depths mainly because of the neglect of the significant vertical heterogeneity in the soil hydraulic properties

variability of gardner s α for coarse textured sediments vadose zone soils in arid regions often contain a high gravel fraction 2 mm size this paper examines for coarse textured soils variability of the slope of gardner s 1958 unsaturated hydraulic conductivity k versus matric potential relation k kse the steady state head control method was used to obtain unsaturated k for tensions as high as 386 cm a total of 79 samples were analyzed in the laboratory the gravel fraction for the 41 gravelly samples ranged from 20 to 71 by weight the remaining 38 samples were sandy with no gravel fraction the measured k values for the gravelly samples fall within a narrow range and are well within the range of measured k values for the sandy samples the bulk of both gravelly and sandy samples can be described using a single slope exponential model gardner s and the intercept k0 are based on a least squares fit to the late time measurements at lower the mean and variance of for the gravelly samples are lower compared with the sandy type the values for the gravelly soils follow a normal distribution whereas the k0 estimates and the laboratory measured ks follow lognormal distributions for the sandy type k0 and ks follow lognormal distributions the values appear to be related to the median particle diameter d50 and the slope of the particle size distribution a clear reduction in variability of is apparent with an increase in d50 suggesting that the unsaturated k and variability for the gravelly soils can be estimated within narrow ranges the flow weighted characteristic pore size m is clearly dependent on the soil type m values for the gravelly soils are characterized by a smaller mean and variance than for the sandy type this helps explain the finding that the range in unsaturated k for the gravelly soils is less than for the sandy type at higher tensions the mean and variance of and lnk0 as well as the cross correlation between and lnk0 are important inputs to stochastic models of unsaturated flow the implications of their variability on flow in heterogeneous media are discussed

geochemistry of dissolved and suspended loads of the seine river france anthropogenic impact carbonate and silicate weathering this study focuses on the chemistry of the seine river system one of the major rivers in europe and constitutes the first geochemical investigation of both suspended and dissolved loads of this river the seine river drains a typical mesozoic cenozoic sedimentary basin the paris basin constituted of limestones mixed or interbedded with terrigenous sediments derived from the paleoreliefs bordering the mesozoic and cenozoic seas in the context of quantifying the global influence of carbonate and silicate weathering on atmospheric co2 consumption the seine river offers the possibility of examining weathering rates in a flat sedimentary environment under temperate climatic conditions one of the major problems associated with the seine river as with many temperate rivers is pollution we propose in this paper 2 approaches in order to correct the dissolved load of the seine river for anthropogenic inputs and to calculate weathering rates of carbonates and silicates the first uses the dissolved load of rivers and tries to allocate the different solutes to different sources a mixing model based on elemental ratios is established and solved by an inversion technique the second approach consists in using the suspended load geochemistry under steady state conditions we show that the geochemistry of suspended sediments makes it possible to estimate the amount of solutes released during the chemical weathering of silicates and thus to calculate weathering rates of silicates the total dissolved load of the seine river at paris can be decomposed into 2 of solutes derived from natural atmospheric sources 7 derived from anthropogenic atmospheric sources 6 derived from agriculture 3 derived from communal inputs and 82 of solutes derived from rock weathering during high floods the contribution of atmospheric and agriculture inputs predominates the weathering rate of carbonates is estimated to be 48 t km2 yr 25 mm 1000 yr only 10 of carbonates are transported in a solid form the rest being transported in solution co2 consumption by carbonate weathering approaches 400 103 mol km2 yr in the seine river at paris about 2 3 mg l of dissolved cations are found to originate from the chemical weathering of silicates by taking dissolved silica into accounts the total dissolved load derived from silicate weathering is about 6 7 mg l this value is minimal because biological uptake of silica probably occur in the seine river the chemical weathering rate of aluminosilicates is estimated to be 2 t km2 yr the ratio of physical over chemical weathering of silicates range between 1 and 3 and the total chemical and physical erosion rates of sedimentary silicates are about 2 3 mm kyr the co2 consumption by silicate weathering 15 24 103 mol km2 yr and is independent of dissolved silica concentration silicate consumption is thus 20 times less than carbonate consumption in the paris basin compared to the neighboring granitic areas the sedimentary region drained by the seine river has 2 to 3 times lower co2 consumption rates we attribute this difference to the cation depleted nature of the seine basin aluminosilicates which are of sedimentary origin at a world scale the chemical denudation rates found for the seine basin are very low and comparable to those given for tropical lowland rivers draining silicates such as the rivers of the congo and amazon basins in spite of huge climatic differences we attribute this similarity to the low mechanical denudation that characterizes these two types of regions

contributions of water rock interactions to the composition of groundwater in areas with a sizeable anthropogenic input a case study of the waters of the fundao area central portugal we used a combination of a grouping algorithm and a weathering algorithm to assess the contributions made by chemical weathering and anthropogenic inputs to the groundwater composition in a granitoid area the first algorithm is based on the mathematical concept of equivalent relations between objects and is used to find groups of water samples using the grouping algorithm we identified groups with similar chemistries in a set of data relating to the water composition in 160 springs and wells in the fundao area portugal the second algorithm is based on stoichiometries mass and charge balances in weathering reactions and is used to relate the water composition of each identified group to water mineral interactions in the area background information on the petrology and mineralogy of the area allowed us to choose the most realistic water mineral interactions we also had information about the use and composition of fertilizers in this agricultural area in applying the weathering algorithm we considered all dissolved silica and bicarbonate to be produced by chemical weathering and all dissolved chloride sulphate and nitrate to be derived from other sources mainly from fertilizers the anthropogenic contributions to the water chemistries in the area are high despite the high background concentrations derived from pollution we were able to assess the contribution of weathering to the water chemistries we obtained realistic results with the two algorithms supported by the fact that the spatial distribution of the samples belonging to the various groups shows a good correlation with the geology and petrology of the area

silicate rock weathering and atmospheric soil co2 uptake in the amazon basin estimated from river water geochemistry seasonal and spatial variations abstract using the data of the camrex project 1982 1984 on the water geochemistry of the amazon river and its main tributaries it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric soil co2 taking into account seasonal and spatial variations this study confirms the important role of the andes in the fluvial transport of dissolved and particulate material by the amazon and it shows for the first time that the silicate weathering rate and atmospheric soil co2 consumption are higher in the andes than in the rest of the amazon basin the seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge the average weathering rate estimated for the whole amazon basin 15 m my is comparable to other estimations made for other tropical equatorial environments a comparison between physical and chemical weathering rates of silicate rocks for the amazon basin and for each tributary basin show that in the andes and in the amazon trough the soil thicknesses are decreasing whereas in the shield the soil profiles are deepening

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

weathering of lower crustal rocks in the kaveri river catchment southern india implications to sediment geochemistry in the upper catchment of the kaveri river in the sahyadri mountains of southern india middle to lower crustal archean granulite grade mafic and felsic rocks with similar structures and textures are exposed under the conditions of active tectonics high rainfall and thick tropical vegetation occurrence of the two major rock types in close association under identical geological geographical and biological conditions provides an uncommon situation for the study of weathering elemental mobilization and sediment generation processes field observations mineralogical and geochemical data including major trace and rare earth elements ree of fresh rocks and variably weathered saprolite samples suggest that close association of mafic and felsic rocks accelerates the denudational processes by early weathering of mafic minerals in felsic rocks and mafic rocks in the terrain due to differential weathering of rocks unweathered to less weathered felsic grains are likely transferred to the coarser fraction of fluvial sediments deposited on the floodplains of the river imposing an upper continental crust ucc geochemical signature it is found that during chemical weathering in addition to other factors weatherability of host minerals of ree control the mobility of ree in the weathering profile it is suggested from the observations on the weathering process and on the geochemistry of derivative sediments that in a tectonically active system with a climate maximum as in sahyadris an equilibrium could be dynamically maintained between weathering and erosional regimes also we infer from our study that there exist certain commonalities between surface denudational and mantle magmatic geochemical differentiation processes similarity of these processes therefore may have implication to common ucc like geochemistry of post archean sediments

modelling the chemical weathering fluxes at the watershed scale in the tropics mule hole south india relative contribution of the smectite kaolinite assemblage versus primary minerals we investigate the chemical weathering processes and fluxes in a small experimental watershed sew through a modelling approach the study site is the mule hole sew developed on a gneissic basement located in the climatic gradient of the western ghats south india the model couples a lumped hydrological model simulating the water budget at the watershed scale to the witch model estimating the dissolution precipitation rates of minerals using laboratory kinetic laws forcing functions and parameters of the simulation are defined by the field data the coupled model is calibrated with stream and groundwater compositions through the testing of a large range of smectite solubility and abundance in the soil horizons we found that despite the low abundance of smectite in the dominant soil type of the watershed 4 vol their net dissolution provides 75 of the export of dissolved silica while primary silicate mineral dissolution releases only 15 of this flux overall smectites modelled as montmorillonites are not stable under the present day climatic conditions furthermore the dissolution of trace carbonates in the saprolitic horizon provides 50 of the calcium export at the watershed scale modelling results show the contrasted behavior of the two main soil types of the watershed red soils 88 of the surface are provider of calcium while black soils smectite rich and characterized by a lower drainage consumes calcium through overall carbonate precipitation our model results stress the key role played by minor accessory minerals and by the thermodynamic properties of smectite minerals and by the drainage of the weathering profiles on the weathering budget of a tropical watershed c 2010 elsevier b v all rights reserved

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

silicate weathering and co2 consumption deduced from the seven chinese rivers originating in the qinghai tibet plateau abstract we present river chemical data for the seven chinese rivers the jinsha jiang yalong jiang min jiang dadu he lancang jiang nu jiang and huang he originating in the qinghai tibet plateau our sampling locations are near sites where the seven rivers flow down the plateau water samples were collected in both high water periods summer and low water periods winter our study shows that most of the ca mg and hco 3 in the seven rivers are derived from the carbonate weathering and only small fractions 10 of the cations are derived from silicate weathering the chemical erosion rates of silicate and carbonate range from 1 1 mm ka 1 to 3 4 mm ka 1 and from 7 5 mm ka 1 to 29 9 mm ka 1 respectively the long term co 2 consumption by silicate weathering in the seven chinese river basins ranges from 0 7 10 5 mol km 2 a 1 to 3 7 10 5 mol km 2 a 1 based on our analysis of chemical data from the seven chinese rivers and the previously published data of the ganges brahmaputra and indus the main ten rivers originating in the himalaya and qinghai tibet plateau consume 328 10 9 mol a 1 of atmospheric co 2 this is only 3 8 of the co 2 consumption derived from global silicate weathering 8700 10 9 mol a 1 indicating that the chemical weathering of the himalaya and qinghai tibet plateau makes a very small contribution to the reduction of the global atmospheric co 2 concentration

slow advance of the weathering front during deep supply limited saprolite formation in the tropical highlands of sri lanka abstract silicate weathering initiated by major mineralogical transformations at the base of ten meters of clay rich saprolite generates the exceptionally low weathering flux found in streams draining the crystalline rocks of the mountainous and humid tropical highlands of sri lanka this conclusion is reached from a thorough investigation of the mineralogical chemical and sr isotope compositions of samples within a regolith profile extending 10 m from surface soil through the weathering front in charnockite bedrock a high grade metamorphic rock corestones formed at the weathering front as well as from the chemical composition of the dissolved loads in nearby streams weatherable minerals and soluble elements are fully depleted at the top of the profile showing that the system is supply limited such that weathering fluxes are controlled directly by the supply of fresh minerals we determine the weathering rates using two independent means 1 in situ produced cosmogenic nuclides in surface soil and creek sediments in the close vicinity of the regolith combined with immobile element mass balance across the regolith and 2 river dissolved loads silicate weathering rates determined from both approaches range from 16 to 36 t km 2 y 1 corresponding to a weathering front advance rate of 6 14 mm ky 1 these rates agree across the 10 1 to 10 4 y time scales over which our rate metrics integrate suggesting that the weathering system operates at steady state within error these rates are furthermore compatible with those obtained by modeling the advance rate of the weathering front from chemical gradients and mineral dissolution rates the silicate weathering flux out of the weathering profile measured on small creeks amounts to 84 of the profile s export flux the remaining 16 is contributed by non silicate atmospheric derived input the silicate weathering flux as measured by dissolved loads in large catchments amounts to ca 50 of the total dissolved flux the remainder being contributed by dust rain and weathering of local marble bands spheroidal weathering is the key processes of converting the fresh bedrock into saprolite at the weathering front the mineralogical composition of weathering rinds shows that the sequence of mineral decomposition is pyroxene plagioclase biotite k feldspar observable biotite alteration does not appear to initiate spheroidal weathering within corestones therefore we infer that other processes than biotite oxidation like pyroxene oxidation clay formation from pyroxene and plagioclase decomposition the development of secondary porosity by plagioclase dissolution or even microbiologic processes at depth enable the coupling between slow advance of the weathering front and slow erosion at the surface the comparison to tectonically more active tropical landscapes lets us conclude that the combination of hard rock with tightly interlocked mineral grains and slow erosion in the absence of tectonically induced landscape rejuvenation lead to these exceptionally low weathering rates

chemical and physical weathering in the min jiang a headwater tributary of the yangtze river abstract the min jiang is a major headwater tributary of the yangtze chang jiang its source is in the undeveloped eastern tibetan plateau but it flows through the heavily populated sichuan four rivers basin on its way to join the yangtze main channel the dissolved major element composition was determined in the tibetan headwaters at the rising stage and at four hydrologic stations in a monthly time series the min jiang is alkaline and has high dissolved load compared to other world rivers carbonate weathering dominates especially in the source region of the min jiang main channel and silicate weathering and evaporite dissolution gain some importance in the dadu he tributary the si na k ratios of the dissolved load and the clay mineralogy of the bed material suggest that silicate weathering in the watershed is superficial i e soluble cations are being preferentially leached many major elements show lower concentrations at high summer discharge but there is also additional input such that the concentration discharge relationship is not purely a result of dilution the discharge weighted total dissolved solid tds flux based on data from the three upstream monitoring stations is 10 10 6 tons year 6 of the yangtze at mouth and the chemical denudation rate as measured by tds yield is 115 tons km 2 year for the min jiang higher than the average yangtze basin 85 tons km 2 year the common extrapolation using annual average discharge and spot sampling of dissolved and suspended material during rising or falling stage can reasonably estimate chemical fluxes to 20 but seriously underestimate the physical flux sampling the peak flash flow is critical for the suspended particulate material concentrations of so 4 cl and ca are significantly elevated as the river debouches onto the populated sichuan basin

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

chemical weathering in the upper huang he yellow river draining the eastern qinghai tibet plateau we examined the fluvial geochemistry of the huang he yellow river in its headwaters to determine natural chemical weathering rates on the northeastern qinghai tibet plateau where anthropogenic impact is considered small qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution most samples are supersaturated with respect to calcite dolomite and atmospheric co2 with moderate 0 710 0 715 87 sr 86 sr ratios while six out of 21 total samples have especially high concentrations of na ca mg cl and so4 from weathering of evaporites we used inversion model calculations to apportion the total dissolved cations to rain evaporite carbonate and silicate origin the samples are either carbonate or evaporite dominated but the relative contributions of the four sources vary widely among samples net co2 consumption rates by silicate weathering 6 120 10 3 mol km 2 yr are low and have a relative uncertainty of 40 we extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide the ganges brahmaputra draining the himalayan front has higher co2 consumption rates 110 570 10 3 mol km 2 yr and more radiogenic 87 sr 86 sr 0 715 1 24 than the upper huang he but the rivers at higher latitudes are similar to or lower than the upper huang he in co2 uptake by silicate weathering in these orogenic zones silicate weathering rates are only weakly coupled with temperature and become independent of runoff above 800 mm yr copyright 2005 elsevier ltd

major ion geochemistry of the nansihu lake basin rivers north china chemical weathering and anthropogenic load under intensive industrialization to explore the chemical weathering processes and the anthropogenic disturbance of weathering 20 water samples were collected from the tributaries in the nansihu lake basin a growing industrial area the major ions in river waters were analyzed to identify and quantify the contributions of the different reservoirs based on stoichiometric analyses and end member determination the contributions of individual reservoirs were calculated for each tributary in the study region the averaged contributions of atmospheric inputs anthropogenic inputs evaporite weathering carbonate weathering and silicate weathering were 2 37 28 25 and 8 respectively combined with information regarding runoff and drainage area the annual average contribution of tds to waters was estimated to be 1 90 0 95 ton km2 from silicate weathering 5 68 2 84 ton km2 from carbonate weathering furthermore the associated consumption of co2 was calculated to be approximately 7 50 109 mol a the industrial and mining activities were the main sources for anthropogenic inputs and they produced non co2 acids nca of all protons involved in chemical weathering 34 was presumed to be originated from nca causing 2 74 109 mol a of co2 degassing moreover industrial inputs could play a major role in the modification of the chemicals in the water system and they could even change the carbonate weathering rate in such an intensively industrializing region in north china the chemical weathering associated with nca was found to be significant for the first time

the indus river system india pakistan major ion chemistry uranium and strontium isotopes the indus river is one of the large river systems draining the himalaya we report in this paper the major ion chemistry sr and u isotope systematics of the indus system particularly its headwaters the results show that 1 on an average about a third of the cations in the waters can be from silicate weathering however most of the ca mg is likely to be from the weathering of carbonates and evaporites 2 the 87sr86sr of the waters ranges between 0 7085 and 0 7595 the higher values 0 72 are typical of the tributaries draining the precambrian granite gneissic terrains the 87sr86sr of the indus main channel throughout its entire stretch shows only minor variations 0 7104 0 7116 the indus transports 8 8 106 mol sr to the arabian sea annually with a 87sr86sr of 0 7111 if our results of sr concentration and 87sr86sr measured at thatta can be considered typical of the indus throughout the year and 3 the u concentration in the indus and its tributaries is generally high 0 37 10 3 g 1 1 the source for the high uranium can be the weathering of granites zones of uranium mineralisation and black shales the indus results when compared with our earlier data on the ganga brahmaputra show that in all these three river systems carbonate weathering is the dominant source of ca mg and hco3 and that u concentrations are high in the case of 87sr86sr the indus waters are less radiogenic however its tributaries draining the precambrian granites gneisses have 87sr86sr in excess of 0 72 similar to that in the rivers of the ganga system the low 87sr86sr of the indus 0 7111 suggests that its contribution to the sr isotope evolution of oceans since the cenozoic is less significant than that of the ganga brahmaputra

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

solute generation and co2 consumption during silicate weathering under subtropical humid climate northern okinawa island japan abstract the chemical characteristics of freshwaters draining the silicate rocks in the northern part of okinawa island were studied to understand solute generation processes and to determine rates of chemical weathering and co2 consumption it was observed that the water chemistry is highly influenced by marine aerosols contributing more than 60 of total solute significant positive correlations observed for chloride versus dissolved silica and chloride versus bicarbonate suggest a strong influence of evapotranspiration on the seasonality of solute concentration it was also found that chemical weathering has been highly advanced in which the dominant kaolinite minerals are being gibbsitized carbonic acid was found to be the major chemical weathering agent releasing greater than 80 of weathering derived dissolved cations and silica while the remaining portion was attributed to weathering by sulfuric acid generated via oxidation of pyrite contained in the rocks the flux of basic cations weathering derived silica and co2 consumption were relatively high due to favourable climatic condition topography and high rate of mechanical erosion silicate weathering rates for basic cations were estimated to be 6 7 9 7 ton km 2 y 1 carbon dioxide consumed by silicate weathering was 334 471 kmol km 2 y 1 which was slightly higher than that consumed by carbonate weathering in general divalent cations mg and ca and bicarbonate alkalinity derived from carbonate dissolution were higher than those from silicate weathering as a consequence the evolution of chemical species in the freshwaters of northern area of okinawa island to a large extent could be explained by mixing of two components characterized by waters with na and cl as predominant species and waters enriched with ca2 and hco3

spatial correlation of permeability in cross stratified sediment with hierarchical architecture 1 cross stratified deposits can give rise to a hierarchy of permeability modes across scales corresponding to a hierarchy of sedimentary unit types the shape of the sample semivariogram for permeability can be largely controlled by the shape of the cross transition probabilities of unit types having the greatest contrast in permeability the shape of those cross transition probabilities can be in turn largely determined by the variance of the lengths of those unit types a sufficient condition for an exponential like semivariogram is the repeated occurrence of unit types having both a contrast in permeability and a large length variance these relationships are shown through writing the identities for spatial correlation of permeability in a hierarchical and multimodal form and as a function of the transition probabilities for the sedimentary unit types these relationships are also illustrated through analyzing data representing cross stratified sediments within a point bar deposit

stochastic analysis of transient flow in unsaturated heterogeneous soils a stochastic unsaturated water flow model is developed for heterogeneous soils subject to a transient flow regime equations are developed for a fully three dimensional soil profile and results are presented for an example one dimensional problem the model predicts the mean and covariance of the soil water content darcy s flux and pore water velocity as a function of the boundary flux and saturated hydraulic conductivity statistics the statistics of the pore water velocity can be used to predict solute transport in soils as shown by foussereau et al this issue approximate flow related moment equations are solved analytically in the laplace domain then the analytical results are numerically inverted using a modified fast fourier transform algorithm the model predictions are compared to results obtained from monte carlo simulations for two different boundary flux patterns characteristic of humid climates and two different soil types a fine sand and a sandy loam comparing the approximate solutions of the statistical moments to the outputs of the monte carlo simulations shows 1 the dominance of the boundary flux variability over that of the saturated conductivity on the overall prediction uncertainty particularly at shallow depths and 2 the good performance of the stochastic unsaturated flow model particularly for fine textured soils subject to boundary fluxes with coefficients of variation up to 1 5 as the boundary flux coefficient of variation increases and the soil becomes coarser the model performance deteriorates because the flow system becomes significantly more nonlinear

first order and numerical analyses of flow and transport in heterogeneous bimodal variably saturated formations 1 addressed here are bimodal heterogeneous variably saturated formations viewed as mixtures of two populations background soil and embedded soil of differing spatial structures two distinct cases are considered in the first case the texture of the embedded soil is finer than that of the background soil in the second case the reverse is true first order lagrangian stochastic analysis of vadose zone transport was used to investigate the combined effect of the texture of the embedded soil and the mean pressure head on solute spread and breakthrough in these formations the main results of the first order analysis suggest that features of solute transport associated with the two different formations exhibit a crossover behavior and that the mean pressure head associated with the crossover may be estimated from the asymptotic macrodispersivities associated with the two formations the applicability of the results of the first order analysis to more realistic conditions was tested with a series of detailed numerical simulations of the flow and transport in three dimensional heterogeneous bimodal variably saturated formations relatively simple steady state flow and more complicated transient nonmonotone flow originating from periodic influx and water uptake by plant roots were considered for the steady state flows results of the simulations were in qualitative agreement with the results of the first order analysis for the more realistic flow regime the results of the simulations suggested that the difference between the responses of the two different bimodal formations might decrease substantially similar to the situation in steady state flow associated with mean pressure head at which a crossover occurs

cosmogenic nuclide evidence for low weathering and denudation in the wet tropical highlands of sri lanka 1 some of the lowest weathering and erosion rates in any mountain range in the world have been measured using cosmogenic nuclides in the steep humid tropical highlands of sri lanka the total preanthropogenic denudation rates were measured in creek sediments and soil samples from unperturbed rain forest sites bedrock from mountain crests and bedrock from inselbergs denudation rates are in the range of 5 30 t km 2 yr 1 2 11 mm ky 1 these rates average denudation over the last 50 250 ky weathering exports in rivers draining the mountainous central highlands show that silicate weathering rates are also low varying from 5 to 20 t km 2 yr 1 today 2 7 mm ky 1 but they represent a significant fraction of the total denudation all these observations run contrary to the conventional geomorphologic and geochemical wisdom that would predict rapid erosion for highlands of high relief temperatures and precipitation we speculate that the high relief in sri lanka represents the remnant of a geomorphic block that was uplifted during rifting at 130 ma or even earlier and that was reduced to the interior of the island by rapid receding of escarpments after continental breakup it is possible that throughout this history hillslopes where not exposing bare bedrock were protected by thick weathered profiles such clay rich layers would inhibit silicate weathering by shielding bedrock from weathering agents in the absence of landscape rejuvenation physical erosion rates are low and fresh mineral surfaces are not being supplied the observation that wet steep tropical highlands can have low rates of rock weathering and erosion has some potentially profound implications for the long term controls of atmospheric co2 budgets high temperature and precipitation which are much invoked though controversial agents for silicate dissolution and co2 drawdown become ineffective in promoting weathering in areas that are not tectonically active

chemical erosion in the eastern himalaya major ion composition of the brahmaputra and δ13c of dissolved inorganic carbon abstract major ion composition of waters 13 c of its dic dissolved inorganic carbon and the clay mineral composition of bank sediments in the brahmaputra river system draining india and bangladesh have been measured to understand chemical weathering and erosion and the factors controlling these processes in the eastern himalaya the time series samples collected biweekly at guwahati from the brahmaputra mainstream were also analyzed for the major ion composition clay mineralogy and chemical index of alteration cia of sediments suggest that weathering intensity is relatively poor in comparison to that in the ganga basin this is attributed to higher runoff and associated physical erosion occurring in the brahmaputra basin the results of this study show for the first time spatial and temporal variations in chemical and silicate erosion rates in the brahmaputra basin the subbasins of the brahmaputra watershed exhibit chemical erosion rates varying by about an order of magnitude the eastern syntaxis basin dominates the erosion with a rate of 300 t km 2 y 1 one of the highest among the world river basins and comparable to those reported for some of the basaltic terrains in contrast the flat cold and relatively more arid tibetan basin undergoes much slower chemical erosion 40 t km 2 y 1 the abundance of total dissolved solids tds 102 203 mg l in the time series samples collected over a period of one year shows variations in accordance with the annual discharge except one of them cause for which is attributable to flash floods na na corrected for cyclic component shows a strong positive correlation with si indicating their common source silicate weathering estimates of silicate cations na sil k sil ca sil mg sil suggest that about half of the dissolved cations in the brahmaputra are derived from silicates a proportion higher than that for the ganga system the co 2 consumption rate due to silicate weathering in the brahmaputra watershed is 6 10 5 moles km 2 y 1 whereas that in the eastern syntaxis subbasin is 19 10 5 moles km 2 y 1 similar to the estimates for some of the basaltic terrains this study suggests that the eastern syntaxis basin of the brahmaputra is one of most intensely chemically eroding regions of the globe and that runoff and physical erosion are the controlling factors of chemical erosion in the eastern himalaya

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

quantitative and qualitative insights into bedrock landform erosion on the south indian craton using cosmogenic nuclides and apatite fission tracks due to the scarcity of datable chronostrati graphic markers and the related difficulties of quantifying depths of erosion in cratonic landscapes conceptual models of tropical pediplain and etchplain evolution commonly lack time and vertical elevation scales here we present the first quantitative study of relief development in south india based on in situ produced 10 be dating aided by previously acquired apatite fission track data erosion rates measured on the summits of inselbergs concur with the perception of inselbergs as islands of low erosion but they also reveal a critical contrast between slowly evolving 2 m m y higher relief landforms and more rapidly eroding 8 12 m m y lower relief landforms this relationship is independent of lithology and climate but suggests that erosion rates on the surrounding plain which are controlled by fluvial incision rates into the plateau surface feed back on inselberg dynamism a discussion on the most suitable sites for dating bedrock land forms highlights the problems of sampling design the difficulties of linking measured erosion rates to the minutiae of process and the limitations of both single and multiple chronometer denudation chronologies in low energy cratonic environments

characterization of groundwater chemistry under the influence of lithologic and anthropogenic factors along a climatic gradient in upper cauvery basin south india hydrogeological and climatic effect on chemical behavior of groundwater along a climatic gradient is studied along a river basin semi arid 500 800 mm of mean annual rainfall sub humid 800 1 200 mm year and humid 1 200 1 500 mm year are the climatic zones chosen along the granito gneissic plains of kabini basin in south india for the present analysis data on groundwater chemistry is initially checked for its quality using nicb ratio 40 of pollution and eliminated for the characterization piper s diagram with mean concentrations indicates the evolution of canahco3 semi arid from cahco3 humid zone along the climatic gradient carbonates dominate other anions and strong acids exceeded weak acids in the region mule hole sew an experimental watershed in sub humid zone is characterized initially using hydrogeochemistry and is observed to be a replica of entire sub humid zone with 25 wells extension of the studies for the entire basin 120 wells showed a chemical gradient along the climatic gradient with sub humid zone bridging semi arid and humid zones ca na molar ratio varies by more than 100 times from semi arid to humid zones semi arid zone is more silicaceous than sub humid while humid zone is more carbonaceous ca cl 14 along the climatic gradient groundwater is undersaturated humid saturated sub humid and slightly supersaturated semi arid with calcite and dolomite concentration depth profiles are in support of the geological stratification i e 18 m of saprolite and 25 m of fracture rock with parent gneiss beneath all the wells are classified into four groups based on groundwater fluctuations and further into deep and shallow based on the depth to groundwater higher the fluctuations larger is its impact on groundwater chemistry actual seasonal patterns are identified using recharge discharge concept based on rainfall intensity instead of traditional monsoon non monsoon concept non pumped wells have low na cl and ca cl ratios in recharge period than in discharge period dilution few other wells which are subjected to pumping still exhibit dilution chemistry though water level fluctuations are high due to annual recharge other wells which do not receive sufficient rainfall and are constantly pumped showed high concentrations in recharge period rather than in discharge period anti dilution in summary recharge discharge concept demarcates the pumped wells from natural deep wells thus characterizing the basin

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

present weathering rates in a humid tropical watershed nsimi south cameroon the study of biogeochemical and hydrological cycles in small experimental watersheds on silicate rocks common for the temperate zone has not yet been widely applied to the tropics especially humid areas this paper presents an updated database for a six year period for the small experimental watershed of the mengong brook in the humid tropics nsimi south cameroon this watershed is developed on precambrian granitoids north congo shield and consists of two convexo concave lateritic hills surrounding a large flat swamp covered by hydromorphic soils rich in upward organic matter mineralogical and geochemical investigations were carried out in the protolith the saprolite the hillside lateritic soils and the swamp hydromorphic soils biomass chemical analyses were done for the representative species of the swamp vegetation the groundwater was analysed from the parent rock saprolite weathering front to the upper fringe in the hillside and swamp system the chemistry of the wet atmospheric and throughfall deposits and the mengong waters was monitored in the nsimi watershed the carbon transfer occurs primarily in an organic form and essentially as colloids produced by the slow biodegradation of the swamp organic matter these organic colloids contribute significantly to the mobilization and transfer of fe al zr ti and th in the uppermost first meter of the swamp regolith when the organic colloid content is low i e in the hillside groundwater th and zr concentrations are extremely low 3 pmol l icp ms detection limits strongly insoluble secondary thorianite tho 2 and primary zircon zrsio 4 crystals control their mobilization respectively this finding thus justifies the potential use of both these elements as inert elements for isoelement mass balance calculations pertaining to the hillside regolith chloride can not be used as a conservative tracer of hydrological processes and chemical weathering in this watershed biogenic recycling significantly influences the low cl input fluxes sodium is a good tracer of chemical weathering in the watershed the sodium solute flux corrected from cyclic salt input was used to assess the chemical weathering rate even though low 2 8 mm kyr the chemical weathering rate predominates over the mechanical weathering rate 1 9 mm kyr compared to the rio icacos watershed the most studied tropical site the chemical weathering fluxes of silica and sodium in the mengong are 16 and 40 times lower respectively this is not only related to the protective role of the regolith thick in both cases but also to differences in the hydrological functioning this is to be taken into account in the calculations of the carbon cycle balance for large surfaces like that of the tropical forest ecosystems on a stable shield at the global level

atmospheric input vs in situ weathering in the genesis of calcretes an sr isotope study at galvez central spain strontium isotopes have been analyzed in a typical calcrete profile developed on granite in the toledo mountains central spain the pedogenic carbonates show clear petrographic evidence of pseudomorphic replacement of the weathered parent granite calcretes display 87sr 86sr ratios between 0 70961 and 0 71059 in sharp contrast to the granite whole rock 0 72856 and minerals 0 71359 to 0 91351 this difference shows that the contribution of sr from the granite to the calcretes is at most 33 and may be as low as 3 direct measurements in rains and aerosols show that the allochtonous source of ca and sr is clearly related to the atmospheric input mainly as dry deposit a slight decrease of sr concentration is observed from the upper horizon composed of continuous calcrete to the deeper calcrete veins in the saprolite this may be due to a kinetic control of the sr ca fractionation and different crystallization rates of the carbonates in the different units of the profile finally local groundwaters have sr isotopic compositions similar to the calcretes and the atmospheric input very different from waters running on the granite

chemical weathering and associated co2 consumption in the godavari river basin india abstract the study gives insight into the source of major ions concentration and their seasonal variability chemical weathering rates and associated co 2 consumption in the godavari river basin grb the results show that the godavari river basin water was mildly alkaline with a wide range of tds 40 to 550 mgl 1 the most dominant anion was hco 3 followed by cl and the most dominant cation was ca 2 followed by na for all three sampling seasons the average molar ratio of cl na was 0 59 in pre monsoon 0 51 for post monsoon and 0 66 in monsoon which is lower than the values reported in earlier studies the range of precipitation corrected molar ratio for ca 2 na was 0 20 to 1 84 in pre monsoon 0 59 to 1 59 in post monsoon and 0 35 to 2 09 in monsoon season mg 2 na was 0 26 to 1 18 0 24 to 0 62 and 0 17 to 1 42 in pre monsoon post monsoon and monsoon respectively while hco 3 na was 2 08 to 7 0 in pre monsoon 1 98 to 4 05 in post monsoon and 1 67 to 5 79 in monsoon which indicated the influence of basalt weathering on river water chemistry factor analysis indicated the vital role of silicate and carbonate weathering along with atmospheric and anthropogenic input that govern the water chemistry of the grb the chemical weathering rate of grb varied from 17 61 to 68 16 tkm 2 y 1 with an average of 39 49 tkm 2 y 1 in pre monsoon from 27 94 to 65 67 with the average of 42 02 tkm 2 y 1 in post monsoon season and from 17 53 to 62 95 tkm 2 y 1 with an average value of 34 69 tkm 2 y 1 in monsoon the associated co 2 consumption rate due to chemical weathering in the grb was 0 25 10 12 mol y 1 which is 1 04 of the annual global co 2 consumption 24 10 12 mol y 1 by chemical weathering of silicate and carbonate rocks the average annual co 2 drawdown by deccan trap area 5 10 5 km 2 based on co 2 consumption rate due to silicate weathering determined in this study was 0 29 10 12 mol y 1 2 48 of the annual global co 2 consumption 11 7 10 12 mol y 1 by silicate weathering gaillardet j dupre b allegre c j 1999 global silicate weathering and co 2 consumption rates deduced from the chemistry of large rivers chemical geology 159 3 30 the present study was the first attempt to calculate weathering rate of deccan trap using major ion chemistry of the godavari river water the third largest river in india the study further provides the inventory for co 2 consumption on river basin scale which is an important consideration from the point of view of global warming

pathways of calcrete development on weathered silicate rocks in tamil nadu india mineralogy chemistry and paleoenvironmental implications abstract poorly documented yet spectacularly thick and extensive outcrops of calcrete hardpan occur on gneiss in the semiarid region of coimbatore south india the hardpan caps a series of residual plateaux forming the present day continental divide and grades into large expanses of vertisols characteristic calcrete and vertisol profiles were logged along toposequences and sampled for macro and micromorphological study and for chemical and mineralogical composition strontium isotopic analyses revealed that the calcrete is derived from in situ weathering of ca bearing primary minerals of the saprolite which is rich in ankerite ca amphiboles and ca plagioclase the macroscale analysis revealed a range of facies developed within the gneiss saprolite but in terms of relative chronology the nodular hardpan has the longest history two evolutionary pathways leading to nodular hardpan formation have been established the first occurs entirely within a vadose environment whereas the second begins within a phreatic environment before continuing to develop in vadose conditions the ability to identify and map these generic categories of calcrete constitutes a potential tool for reconstructing paleotopography and paleogroundwater levels the bedrock weathering derived nodular hardpan is blanketed by a laminar facies that correlates with an eolian event with marine sr signatures this suggests influx of ca dust from the arabian sea continental shelf during a pleistocene sea level low stand it defines an important benchmark in the chronology of the area and highlights the potential antiquity of the thick calcrete profiles

estimation of weathering rates and co2 drawdown based on solute load significance of granulites and gneisses dominated weathering in the kaveri river basin southern india abstract the solute load of the kaveri river south india and its tributaries draining diverse precambrian terrains during pre monsoon and monsoon periods was determined using average annual flow total drainage area and atmospheric input corrected major ion concentrations of these rivers chemical weathering rates annual fluxes of different ionic species to the ocean and co2 consumption rates were estimated bicarbonate is the most dominant ion 27 79 of anion budget in all the river samples collected during monsoon period followed by ca2 whereas in case of pre monsoon water samples na is the most dominant ion in meq l two approaches were adopted to estimate silicate and carbonate weathering rates in the drainage basin at musuri silicate weathering rate swr is 9 44 0 29 tons km2 a and carbonate weathering rate cwr is 1 46 0 16 tons km2 a more than 90 of the total ionic budget is derived from weathering of silicates in the kaveri basin co2 consumption rate in the basin for silicate weathering f co 2 sil is 3 83 0 12 105 mol km2 a upper limit which is comparable with the himalayan rivers at upper reaches for carbonate weathering f co 2 carb co2 consumption rate is 0 15 0 03 105 mol km2 a in the kaveri basin the lower limit of co2 consumption rate corrected for h2so4 during silicate and carbonate weathering is f co 2 sil is 3 24 1005 mol km2 a and f co 2 carb 0 13 105 mol km2 a respectively co2 sequestered due to silicate weathering in the kaveri basin is 25 41 0 82 109 mol a which represents 0 21 0 01 of global co2 drawdown this may be due to tropical climatic condition high rainfall during both sw and ne monsoon and predominance of silicate rocks in the kaveri basin

isotopic tracers of the origin of ca in a carbonate crust from the middle atlas morocco abstract carbonate crusts developed on basalt were studied at tazouta in the moroccan middle atlas the chosen representative weathering profile is 2 8 m thick and is composed from base to top of a fresh basalt overlain by a coherent saprolite a friable saprolite and a surface soil carbonate crust genesis occurs by replacement of primary and secondary clay minerals by low mg calcite the 14 c dates of the calcite range from 15 to 14 ka in the coherent saprolite and from 12 to 8 5 ka in the friable saprolite smectitic weathering and replacement of si bearing minerals by carbonate are coupled processes leading to a strong calcium net gain 300 kg m 3 within the friable saprolite the low weathering rate of basalt compared to the calcrete genesis rate and the high mobility of calcium in supergene weathering mantles limit the basaltic ca contribution to calcrete genesis the contribution of the triassic sediment is also limited by the mineralogical unavailability of ca the 87 sr 86 sr ratios confirm the low contribution of basalt and indicate an external origin of ca the sr isotope ratios of calcrete are different from those of the adjacent liassic carbonates and are close to rainfall values the carbon isotope compositions of carbonates 8 to 9 vs pdb imply a significant contribution of c3 dominated organic carbon during carbonate precipitation oxygen isotopic compositions of carbonates average 5 24 vs pdb show that carbonates are 18 o enriched compared to meteoric waters 4 to 3 5 vs smow

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

major ion chemistry in the headwaters of the yamuna river system chemical weathering its temperature dependence and co 2 consumption in the himalaya abstract the yamuna river and its tributaries in the himalaya constitute the yamuna river system yrs the yrs basin has a drainage area and discharge comparable in magnitude to those of the bhagirathi and the alaknanda rivers which merge to form the ganga at the foothills of the himalaya a detailed geochemical study of the yrs was carried out to determine i the relative significance of silicate carbonate and evaporite weathering in contributing to its major ion composition ii co2 consumption via silicate weathering and iii the factors regulating chemical weathering of silicates in the basin the results show that the yrs waters are mildly alkaline with a wide range of tds 32 to 620 mg l 1 in these waters the abundances of ca mg and alkalinity which account for most of tds are derived mainly from carbonates many of the tributaries in the lower reaches of the yamuna basin are supersaturated with calcite in addition to carbonic acid sulphuric acid generated by oxidation of pyrites also seems to be supplying protons for chemical weathering silicate weathering in yrs basin contributes on average 25 molar basis of total cations on a basin wide scale silicate weathering however does not seem to be intense in the basin as evident from low si na k in the waters 1 2 and low values of chemical index of alteration cia in bed sediments 60 co2 drawdown resulting from silicate weathering in the yrs basin in the himalaya during monsoon ranges between 4 to 7 105 moles km 2 y 1 this is higher than that estimated for the ganga at rishikesh for the same season the co2 consumption rates in the yamuna and the ganga basins in the himalaya are higher than the global average value suggesting enhanced co2 drawdown in the southern slopes of the himalaya the impact of this enhanced drawdown on the global co2 budget may not be pronounced as the drainage area of the yrs and the ganga in the himalaya is small the co2 drawdown by silicates in the yrs basin is marginally higher than the reported values of co2 release from oxidation of organic rich sediments estimated using re as a proxy this comparison shows the need to constrain co2 sources and sinks better to balance its budget in a regional scale the results also show that silicate weathering rate in the yrs basin is 10 mm ky 1 and on the ganga basin it is 5 mm ky 1 which are several times lower than the carbonate weathering rates the significantly higher silicate weathering rate observed in the yrs basin seems to be governed by rapid physical erosion in this region the apparent activation energy for overall silicate weathering in the yrs basin derived from na and si concentrations and water temperature ranges from 50 to 80 kj mol 1 these values are comparable to those reported for granitoid weathering in natural watersheds and feldspar weathering in laboratory experiments this study brings to light the sources contributing to major ions enhanced chemical weathering rates in the yamuna river basin and interdependence of silicate weathering on physical erosion and temperature