time scales of sedimentary transfer and weathering processes from u series nuclides clues from the himalayan rivers abstract in order to define time scales of erosion and sedimentary transfer in the himalaya 238 u 234 u 230 th disequilibria have been analysed in river bank sediments and in bedloads collected along the kali gandaki river one of the main nepalese rivers and in the ghaghara and gandak rivers two major plain tributaries of the ganges the th activity ratios and u th ratios in river sediments of the two ganges tributaries constantly decrease from upstream to downstream this is related to the maturation of sediments by weathering during their transfer to the plain the u series data allow to calculate a transfer time for the sediments in the alluvial gangetic plain from the chain front to the confluence with the ganges of about 100 kyr for both rivers the kali gandaki river sediment data highlight a decrease of both the th isotopic and u th ratios which is explained by a mixing between two sources with similar u th ratios but having suffered a different u th fractionation history interpretation of the u series data in the frame of this scenario gives long time scales of weathering of several 100 s kyr for the himalayan terranes the results imply that himalayan bedrocks are submitted to a long in situ stage of weathering before their erosion and transfer into the rivers in addition occurrence of similar u sr signatures in dissolved i e

li and δ7li in himalayan rivers proxies for silicate weathering this paper presents the first systematic survey of lithium and its isotopes in the dissolved load and suspended and bed sediments of tributaries of the ganges both before and after the monsoon locations were chosen in order to cover catchments draining both silicates and carbonates at high 2000 4000 m and low 550 1300 m altitudes modelling of the dissolved composition shows that the li ca ratio of the silicate endmember in himalayan rivers is at least an order of magnitude higher than that of the carbonate endmember most of the dissolved li 90 is derived from silicates even in carbonate dominated catchments while the sr isotope composition of the dissolved load reflects that of the bedrock the main control on its li isotope composition is fractionation during weathering fractionation between the dissolved and suspended load in silicate dominated catchments is greatest at high altitude and lower at low altitude where weathering is more intense tributaries draining silicates have lower dissolved 7li values by 2 3 to 4 2 following the monsoon when weathering is more intense because of higher runoff and elevated temperatures our data suggest that riverine li fluxes largely reflect silicate weathering rates while riverine 7li varies with weathering intensity as rivers presently contribute 50 of the li input to the oceans seawater li concentrations and 7li show potential as proxies for global silicate weathering processes

ca sr and 87sr 86sr geochemistry of disseminated calcite in himalayan silicate rocks from nanga parbat influence on river water chemistry trace amounts of disseminated calcite were identified in gneiss schist and granite bedrock sampled from the raikhot watershed and other locations within the nanga parbat massif of northern pakistan the calcite grains occur interstitially within individual silicate minerals at grain boundaries and as fracture fillings that transect the mineralogic fabric of the rock disseminated calcite composes is 0 29 wt of silicate rocks sampled in the raikhot watershed and has ca sr mol nmol and 87sr 86sr ratios that range from 0 878 to 5 33 and from 0 794 039 to 0 930 619 respectively elsewhere in the nanga parbat region disseminated calcite composes 3 6 wt of the silicate rock samples and has ca sr mol nmol and 87sr 86sr ratios that range from 0 535 to 3 33 and from 0 715 757 to 0 771 244 respectively for all samples the 87sr 86sr ratios of disseminated calcite are similar to the 87sr 86sr ratios measured in the silicate host rock within the partially glaciated raikhot watershed the rapid weathering of disseminated calcite with high ca sr and 87sr 86sr ratios has a strong influence on the chemical composition of stream water and exceeds contributions from silicate mineral dissolution comparisons of disseminated calcite compositions with source water chemistry throughout the himalaya suggest that disseminated calcite may be a more important component of himalayan silicate rocks than previously recognized therefore calculations relating the sr isotope geochemistry of himalayan rivers to atmospheric co2 consumption should consider this widespread and compositionally variable carbonate end member

hydrothermal source of radiogenic sr to himalayan rivers 1 k 1 and cl 2 all of which are high in the hydrothermal waters cation concentrations decrease along the lesser himalayan reach of the river hot spring dissolved co2 has a d 13 c value to 15 9 indicating that metamorphic decarbonation reactions contribute co2 to the fluids hydrothermal co2 is partially neutralized in high temperature weathering reactions which generate alkalinity and yield abundant radiogenic sr radiogenic hydrothermal carbonate can form from these solutions and later weather releasing silicate sr but imparting carbonate characteristics to the overall water chemistry

silicate weathering rates decoupled from the 87sr 86sr ratio of the dissolved load during himalayan erosion this study establishes that carbonate weathering dominates the supply of sr with elevated 87sr 86sr ratios in the bhote kosi sun kosi river system central nepal a major himalayan tributary to the ganges the dissolved load of the bhote kosi sun kosi displays a rapid increase in the 87sr 86sr ratio in its lower section downstream of the main central thrust a feature common to other himalayan tributaries of the ganges mass balance analysis of the contributing sources to the dissolved load identifies the weathering of palaeoproterozoic impure carbonates comprised largely of dolomite and mica from the lesser himalaya as the most significant lithological control upon elevated 87sr 86sr ratios in situ laser ablation analysis of the dolomite component yields 87sr 86sr ratios of 0 93 to 1 11 indistinguishable from bulk rock this confirms the presence of a highly soluble source of radiogenic strontium and suggests that diffusive exchange during a protracted metamorphic history has homogenised sr isotopes between silicate and carbonate phases within the assemblage weathering of the carbonate component of such rocks has yielded unusually high 87sr 86sr at significant sr fluxes in the dissolved load approximately 60 of the impact of the bhote kosi sun kosi on the marine 87sr 86sr ratio can be traced to weathering of this carbonate since similar lithologies outcrop within the catchments of most himalayan tributaries that feed the ganges and brahmaputra rivers the presence of such radiogenic carbonates undermines the inference that the impact of these rivers on sr isotopes in seawater is indicative of high silicate weathering rates that result from the uplift of tibet and the himalaya

effect of differential stress on strontium partitioning in calcite abstract strontium content of calcite has been used to aid in the interpretation of diagenesis of carbonate rocks however the distribution coefficient for strontium partitioning between calcite and solution kdsr ca is subject to both kinetic and thermodynamic factors that are incompletely understood the effect of stress which may involve both of these factors on the partitioning of trace element cations in the carbonate lattice has not previously been investigated aragonite to calcite transformation may occur under axial stress burial conditions if aragonite rich sediments escape near surface diagenetic alteration the effect of stress on kdsr ca during aragonite to calcite conversion was investigated through experimental compaction studies experiments investigated partitioning behavior under conditions of purely hydrostatic fluid pressure surrounding growing calcite crystals changes in hydrostatic pressure up to 35 mpa isothermal had little or no effect on the partitioning of strontium into calcite varying solution sr ca ratios at constant temperature likewise had no effect on the distribution coefficient hydrostatic experiments also investigated the temperature dependence of partitioning experimental data indicate that kdsr ca at stp is about 0 028 an experimental design was also constructed to test whether differential stress affects the kdsr ca value a compaction apparatus was used to generate an effective stress of over 5 mpa simulating lithostatic burial load at approximately 240 m temperature was held constant during experimental compaction runs data from compaction experiments show an order of magnitude depression of kdsr ca with increasing effective stress in the range from 0 to 5 35 mpa these empirical results may aid in the interpretation of low sr limestones in the geologic record

the late neogene 87sr 86sr record of lowland himalayan rivers fossil shells and paleosol carbonate from ancestral himalayan river deposits provide a 87 sr 86 sr record of lowland himalayan river water during the late neogene reconstructed 87 sr 86 sr river values increased sharply in the late miocene probably marking the beginning of exhumation of high 87 sr 86 sr metalimestones more in the central than in the western himalayas these results imply that the marine 87 sr 86 sr record may not be a proxy for silicate weathering or consumption of atmospheric co 2 resulting from that weathering

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

proportions of convective and stratiform precipitation revealed in water isotope ratios distinguishing convective and stratiform rainfall is key to understanding how the water cycle responds to climate change an analysis of satellite and surface data shows that rain isotope ratios reflect the proportions of these types of rain

climatic significance of holocene beachrock sites along shorelines of the red sea mozley and burns 2006 discussion reminds me of current discussions on paleotemperature elsewhere in the july 29 2005 issue of science the following statements are presented two teams of researchers studying the same evidence with the same techniques have painted diametrically opposite pictures of a key period in the history of earth s climate which climatologists are probing it s a tough issue to sort out what s at stake is the regional distribution of climate both past and future kerr 2005 p 687 we have to wait for more data this is difficult work and it is easy to be misled before answering specific criticism please note that my study was a geologic note and not a full article my detailed article friedman 2004 was published as part of a special publication series requested by the geochemical society as part of its tribute to isaac r kaplan i refer mozley and burns 2006 to the details of my article i shall answer their criticism the studied beachrock is composed of 1 terrigenous debris derived from nearby bedrock 2 carbonate particles of local origin and 3 carbonate cement friedman 1988 table 1 view this table table 1 x ray diffraction mineralogical analysis the most common beachrock lithology is terrigenous calcipebblestone figure 1 and calcisandstone in which skeletal debris is minor or absent terrigenous rock fragments are dominant and carbonate cement is abundant terrigenous debris does not affect radiocarbon dating nor carbon or strontium isotopic measurements because in most of the samples the debris does not generally contain carbonates the samples selected for the study contain fossils only sporadically or at best fossils are entirely absent figure 1 beachrock with abundant included terrigenous pebbles paving intertidal zone and extending into supratidal zone on the west side of the gulf of aqaba terrigenous particles in the studied beachrocks consist of igneous and

a sequence stratigraphic model for reservoir sand body distribution in the lower permian shanxi formation in the ordos basin northern china abstract the lower permian shanxi formation is the main gas bearing stratigraphic unit in the northeastern ordos basin china based on an integrated investigation of well logs seismic data cores and outcrops the lower member of the shanxi formation has been subdivided into three third order sequences from base to top namely sq1 sq2 and sq3 the three sequences consist primarily of stacked lowstand systems tracts with little deposition of transgressive systems tracts and or highstand systems tracts detailed sedimentological and stratigraphic analyses indicated that the entire sequence is characterized by a regional transgression with incised valleys and channel fills marking the bases of each retro gradational sequence and swamp or inter channel bay mudstone and coal deposits capping each sequence the three sequences retracted source ward sequentially from the sandstone dominated sq1 to the mudstone dominated sq3 the spatial and temporal distributions of the reservoir sandstones was primarily controlled by retro gradational stacking patterns channel sand bodies formed during the lowstand systems tracts of sq1 sq2 and sq3 are excellent reservoirs which form excellent reservoir cap rock assemblages with the overlying fine grained sediments the unique sequence stacking patterns control the accumulation of hydrocarbons the reservoir quality of the sq1 sq2 and sq3 sequences become worse gradually from base to top within each sequence channel or incised valley fill of the lowstand systems tracts remain potential good expiration targets

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

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

isotope evidence for secondary sulfide precipitation along the marsyandi river nepal himalayas abstract we present sulfur and oxygen isotope data from 41 samples of dissolved riverine sulfate from along 65 km of the marsyandi river in the northern himalayas coupled sulfur and oxygen isotopic composition of riverine sulfate 34 s so 4 and 18 o so 4 respectively yield unique constraints on the source of sulfur to the river system the headwaters of the marsyandi river have light 34 s so 4 and 18 o so 4 which requires that the source of sulfate to the river is through the anoxic weathering of pyrite likely via fe3 the 34 s so 4 and 18 o so 4 of sulfate in tributaries to the marsyandi increase downstream which could result either from inputs from evaporites or bacterial sulfate reduction with subsequent sulfide precipitation in warmer and wetter catchments either of these processes could result in heavy 34 s so 4 and 18 o so 4 of the residual river sulfate elemental ratios such as sr ca and ca so4 suggest as previous studies have also concluded that evaporite weathering is not important in the marsyandi river we conclude that the isotope data is most consistent with the onset of bacterial sulfate reduction and secondary sulfide precipitation in the soils in the warmer and wetter downstream catchments our results have implications for understanding the source of sulfate to the ocean as well as the redox and acidity budget within rapidly eroding catchments

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

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

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

major ion chemistry of the yarlung tsangpo brahmaputra river chemical weathering erosion and co2 consumption in the southern tibetan plateau and eastern syntaxis of the himalaya the yarlung tsangpo brahmaputra river drains a large portion of the himalaya and southern tibetan plateau including the eastern himalayan syntaxis one of the most tectonically active regions on the globe we measured the solute chemistry of 161 streams and major tributaries of the tsangpo brahmaputra to examine the effect of tectonic climatic and geologic factors on chemical weathering rates specifically we quantify chemical weathering fluxes and co2 consumption by silicate weathering in southern tibet and the eastern syntaxis of the himalaya examine the major chemical weathering reactions in the tributaries of the tsangpo brahmaputra and determine the total weathering flux from carbonate and silicate weathering processes in this region we show that high precipitation rapid tectonic uplift steep channel slopes and high stream power generate high rates of chemical weathering in the eastern syntaxis the total dissolved solids tds flux from the this area is greater than 520 tons km 2 yr 1 and the silicate cation flux more than 34 tons km 2 yr 1 in total chemical weathering in this area consumes 15 2 10 5 mol co2 km 2 yr 1 which is twice the brahmaputra average these data show that 15 20 of the total co2 consumption by silicate weathering in the brahmaputra catchment is derived from only 4 of the total land

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

sr and 87sr 86sr in waters and sediments of the brahmaputra river system silicate weathering co2 consumption and sr flux abstract the brahmaputra is a major river system draining the himalaya the concentration of sr and its 87 sr 86 sr have been measured in dissolved and particulate phases of the brahmaputra and its tributaries in india to trace the sources of dissolved sr dissolved sr ranges from 250 to 1050 nm with 87 sr 86 sr from 0 71298 to 0 75975 the sr data along with the available concentrations of major ions in the samples show that major contributors of sr in the brahmaputra system are the silicates and carbonates of the himalaya and the transhimalaya and carbonates and evaporites of the tibetan basin silicate sr in the brahmaputra river system ranges from 20 to 80 with an average of 45 the silicate component of sr in the brahmaputra system is similar or marginally higher than that in the ganga system due to contribution from the transhimalayan calc alkaline plutonic rocks which have higher concentration of sr evaporites of the tibetan sub basin and hot springs along the indus tsangpo suture could be the other significant contributors to the dissolved sr budget of the brahmaputra contribution from evaporite dissolution decouples the total dissolved sr flux from the tibetan basin from atmospheric co 2 consumption radiogenic sr of the brahmaputra system is derived from the himalayan silicates whereas other sr sources tend to dilute its radiogenic signature the 87 sr 86 sr of the dissolved phase shows significant correlation with indices of silicate weathering indicating that 87 sr 86 sr can serve as a proxy of silicate weathering at their outflow the brahmaputra is less radiogenic 0 72 compared to the ganga 0 73 however the flux of 87 sr from the brahmaputra is similar to that of the ganga

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

hydrochemical signatures of deep groundwater circulation in a part of the himalayan foreland basin groundwater samples were analyzed from 71 springs and wells as part of a larger study in a region of compressional tectonic regime the study site covers the peshawar basin and surroundings in the himalayan foreland of pakistan the northern portion is mountainous and the water table is discontinuous in different intermontane valleys with abundant springs with normal and anomalous temperatures and composition the southern part is divided into isolated basins with a number of drilled deep and dug shallow wells hydrochemical signatures of elevated strontium sr sio2 boron b and the geothermometric signatures all indicate a deep circulation of the emerging groundwater moreover for several of the sample sites water chemical compositions measured spring and water well temperatures and reservoir temperatures calculated for spring waters all point to origin from deep horizons within the basin remarkable proximity of all the thermal and hydrochemical anomalies to major faults suggests that the waters ascended along these faults from greater depths the area is a natural western extension of the himalayan geothermal belt described in earlier literature for the eastern and central himalayas

geologic control of sr and major element chemistry in himalayan rivers nepal our study of the seti river in far western nepal shows that the solute chemistry of the river and its tributaries is strongly controlled by geology the seti flows through four distinct terranes starting with the tethyan sedimentary series tss and greater himalayan series ghs tss ghs waters display 87 sr 86 sr ratios of 0 73 and high sr and ca consistent with the composition of limestone and marble common in these terranes the 87 sr 86 sr ratio and mg increase markedly as the river passes into the lesser himalayan series lhs where tributaries have 87 sr 86 sr ratios from 0 75 to 1 02 and high sr ca and mg the high mg in lhs waters correlate with high 87 sr 86 sr ratios which we attribute to weathering of highly radiogenic 0 71 0 82 dolostones tributaries to the seti river draining the largely carbonate free dadeldhura thrust sheet dts have ratios near 0 74 but low sr ca and mg and therefore have little impact on seti mainstem chemistry mass balance calculations and camg weathering indices show that carbonate weathering accounts for 70 of total dissolved solids to the seti river sr ca ratios of river waters provide a minimum estimate of the carbonate weathering contribution to sr due to partitioning of sr and ca during incongruent dissolution and reprecipitation of calcite overall we attribute high 87 sr 86 sr ratios in the seti river and its tributaries to the weathering of metacarbonates especially dolostones in the upper nawakhot group which have exchanged sr with silicates during metamorphism our modeling of sr fluxes in the seti river indicates that the tss ghs accounts for 36 39 of the sr the lhs for 40 53 and 8 23 for the dts prior to exposure of lhs rocks at 12 ma tss and ghs carbonates with low 87 sr 86 sr ratios dominated himalayan rivers we attribute the elevated 87 sr 86 sr ratios of himalayan paleorivers during the late miocene and pliocene to exposure and weathering of lhs metacarbonates copyright 2000 elsevier science ltd

findings on water quality in upper mustang nepal from a preliminary geochemical and geological survey the major ion and trace element chemistry of water samples including springs rivers and irrigation ditches collected during a survey on august 2016 in the upper mustang region of the mustang district of dhawalagiri zone nepal has been investigated the upper mustang region a cold desert represents a hot spot for climate change indeed violent hailstorms and rainstorms have been recently observed consequently exposing land to erosion results of this study indicate that waters in the region belong to the ca hco3 ca mg cl so4 and na k cl types reflecting different hydrochemical regimes uranium is widespread in waters with concentrations up to 19 g l recorded in a potable water supply locally anoxic conditions affect uranium mobility due to the low solubility of u iv minerals highly toxic thallium was detected in a thermal spring at an elevated concentration 45 g l tl the association of thallium with high concentrations of iron suggests that these elements are derived from pyrite oxidation detectable levels of thallium were also measured in the water of an irrigation ditch lithium concentrations ranged from 7 g l to 12 mg l in the thermal water and showed a strong association with chloride ions arsenic concentrations up to 4 7 g l were measured in tributaries of the kali gandaki river the data provide evidence that solutes in water have originated from an array of input sources including carbonate dissolution the dissolution of soluble salts silicate weathering and localized sulfide oxidation in particular chemical weathering of granitic rocks is likely the primary source for metals and metalloids in waters since the erosion rate is a factor affecting lithological weathering high intensity rainfalls due to climate change are expected to influence the release and fate of potentially harmful elements in the in the upper mustang valley

competition between erosion and reaction kinetics in controlling silicate weathering rates article i nfo weathering rates of minerals may be limited by the reaction kinetics of the constitutive minerals or the supply of fresh minerals delivered to the near surface by denudation we use a model of denudation and reaction kinetics to analyze the relative importance of each in moderating silicate weathering fluxes in different erosional environments for different commonly occurring silicate minerals we find that minerals that reside in the near surface weathering zone for far longer than the reaction takes to complete as is the case with slow denudation produce weathering fluxes that respond most strongly to changes in denudation rate conversely when transit through the weathering zone is rapid relative to a given mineral s weathering timescale the weathering responds most vigorously to changes in the reaction kinetics based on field and laboratory measured values of silicate weathering kinetic constants observed weathering zone thicknesses in relation to denudation rates and denudation rates inferred from topography it appears that fresh mineral supply may play a sub equal or dominant role in moderating silicate weathering fluxes for four mineral phases considered if correct this suggests that the concentration of atmospheric co2 which is regulated by silicate weathering over geologic timescales may depend on those factors that control long term erosion rates across earth s surface

stable isotopic evidence for mixing between metamorphic fluids and surface derived waters during recent uplift of the southern alps new zealand recent studies have shown that the southern alps of new zealand have active hydrothermal systems driven by tectonic uplift these studies have concentrated on the rapidly exhumed rocks immediately adjacent to the alpine fault we present new stable isotopic evidence that shows that fluid flow and fluid mixing processes thought to be restricted to rocks near the alpine fault also occurred in the low uplift rate region of the southern alps orogen during the kaikouran orogeny 10 ma to present low 18ocalcite values of post metamorphic veins in the eastern southern alps indicate that meteoric waters have penetrated to hot midcrustal levels 350 300 c 5 km depth and mixed with metamorphic fluids in areas far removed from the alpine fault in addition the isotopic values of calcites precipitated in active faults in the mackenzie basin define a trend of increasing 18o decreasing 13c and decreasing temperature and form an isotopic mixing line between fault and vein calcites crosscutting metamorphic rocks and authigenic calcites precipitated in mackenzie basin sediments the isotope data indicate a second phase of mixing between a modified metamorphic fluid and a surficial diagenetic fluid at shallow depths we suggest that mixed metamorphic meteoric hydrothermal systems have developed in the east side of the southern alps during uplift and that active faults have played a critical role in transporting metamorphic fluids outward from the mountain front and into the adjacent intermontane basins

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes

downstream and seasonal changes of lithium isotope ratios in the ganges brahmaputra river system the li isotope ratio 7li is expected to be a useful tracer of silicate weathering in river and groundwater systems which is an important contributor to the seawater compositional changes that accompany the evolution of the earth s surface environment to obtain accurate estimates of continental li fluxes to the ocean we determined 7li values of dissolved li in the lower ganges brahmaputra river system in both the dry and rainy seasons and in deep groundwater in the bengal basin dissolved li and 7li values in the lower reaches of the rivers 0 04 0 66 mol kg 1 and 19 1 to 34 2 respectively were predominantly derived from silicate weathering as is the case in the upper parts of these rivers we observed large changes in 7li over a distance of more than 1000 km downstream that were due mainly to rayleigh type removal of li from river water extremely high li concentrations 1 15 1 67 mol kg 1 and low 7li values 5 1 to 11 6 in groundwater samples indicate congruent isotope leaching and dissolution of silicate minerals in the deep aquifer where the water residence time is long in the rainy season li concentrations and 7li values were lower than in the dry season owing to the shorter residence time of river water and the substantial input of local subsurface flow through lowland alluvium these results suggest that accurate estimation of continental li fluxes to the ocean should take account of downstream and seasonal changes as well as aquifer depth variations in 7li values

temperature dependence of the strontium distribution coefficient in calcite an experimental study from 408 degrees to 2008 degrees c and application to natural diagenetic calcites abstract the temperature dependence of sr coprecipitation with calcite was determined experimentally in solutions with sr ca ratios and ionic strengths closely resembling marine pore fluids aragoniteto calcite and dolomite to calcite transformations were conducted over a temperature range from 40 to 200 c temperature dependence of the distribution coefficient of strontium in calcite dcsr is significant dcsr in aragonite to calcite experiments varied from 0 046 at 40 c to 0 068 at 200 c dcsr in dolomite to calcite experiments varied from 0 034 at 40 c to 0 062 at 200 c experimental values of dcsr are somewhat dependent on the precursor phase the experimental results are applied to natural diagenetic and hydrothermal calcites recovered from the sediment covered middle valley part of the juan de fuca ridge spreading center ocean drilling program holes 857c and 858d low mg calcites from hole 858d have sr contents appropriate for their present day in situ temperatures and pore water sr values in contrast high mg calcites from hole 858d that precipitated from supersaturated pore waters at inferred high growth rates have elevated sr contents relative to calculated equilibrium values the sr contents of calcites from hole 857c are close to predicted equilibrium values in some instances but are substantially different in others deviations from predicted equilibrium sr contents especially in nodules are attributed to the formation of mixed generations of carbonate precipitating with increasing burial depths and temperatures through pore waters with variable sr composition

climatic and tectonic controls on chemical weathering in the new zealand southern alps abstract climatic and tectonic controls on the relative abundance of solutes in streams draining the new zealand southern alps were investigated by analyzing the elemental and sr isotope geochemistry of stream waters bedload sediment and hydrothermal calcite veins the average relative molar abundance of major cations and si in all stream waters follows the order ca2 50 si 22 na 17 mg2 6 k 5 for major anions the relative molar abundance is hco3 89 so42 7 cl 4 weathering reactions involving plagioclase and volumetrically small amounts of hydrothermal calcite define the ionic chemistry of stream waters but nearly all streams have a carbonate dominated ca2 and hco3 mass balance stream water ca sr and 87sr 86sr ratios vary from 0 173 to 0 439 mol nmol and from 0 7078 to 0 7114 respectively consistent with the ionic budget these ratios lie solely within the range of values measured for bedload carbonate ca sr 0 178 to 0 886 mol nmol 87sr 86sr 0 7081 to 0 7118 and hydrothermal calcite veins ca sr 0 491 to 3 33 mol nmol 87sr 86sr 0 7076 to 0 7097 streams draining regions in the southern alps with high rates of physical erosion induced by rapid tectonic uplift and an extremely wet climate contain 10 more ca2 and 30 more sr2 from carbonate weathering compared to streams draining regions in drier more stable landscapes similarly streams draining glaciated watersheds contain 25 more sr2 from carbonate weathering compared to streams draining non glaciated watersheds the highest abundance of carbonate derived solutes in the most physically active regions of the southern alps is attributed to the tectonic exhumation and mechanical denudation of metamorphic bedrock which contains trace amounts of calcite estimated to weather 350 times faster than plagioclase in this environment in contrast regions in the southern alps experiencing lower rates of uplift and erosion have a greater abundance of silicate versus carbonate derived cations these findings highlight a strong coupling between physical controls on landscape development and sources of solutes to stream waters using the southern alps as a model for assessing the role of active tectonics in geochemical cycles this study suggests that rapid mountain uplift results in an enhanced influence of carbonate weathering on the dissolved ion composition delivered to seawater