characterization and migration of atmospheric ree in soils and surface waters abstract rainwater and snow collected from three different sites in france vosges mountains french alps and strasbourg show more or less similar shapes of their ree distribution patterns rainwater from strasbourg is the most ree enriched sample whereas precipitations from the two mountainous less polluted catchments are less ree enriched and have concentrations close to seawater they are all strongly lree depleted different water samples from an alpine watershed comprising snow interstitial puddle and streamwater show similar ree distributions with lree enrichment rainwater normalized but mree and hree depletion in this environment where water transfer from the soil to the river is very quick due to the low thickness of the soils it appears that ree in streamwater mainly originate from atmospheric inputs different is the behaviour of the ree in the spring and streamwaters from the vosges mountains these waters of long residence time in the deep soil horizons react with soil and bedrock ree carrying minerals and show especially significant negative eu anomalies compared to atmospheric inputs their sr and nd isotopic data suggest that most of the sr and nd originate from apatite leaching or dissolution soil solutions and soil leachates from the upper soil horizons due to alteration processes strongly depleted in ree carrying minerals have ree distribution patterns close to those of lichens and throughfall throughfall is slightly more enriched especially in light ree than filtered rainwater probably due to leaching of atmospheric particles deposited on the foliage and also to leaf excretion data suggest that sr and nd isotopes of the soil solutions in the upper soil horizons originate from two different sources 1 an atmospheric source with fertilizer dust and seawater components and 2 a source mainly determined by mineral dissolution in the soil these two different sources are also recognizable in the sr and nd isotopic composition of the tree s throughfall solution the atmospheric contributions of sr and nd to throughfall and soil solution are of 20 to 70 and 20 respectively in springwater however the atmospheric sr and ree contribution is not detectable

strontium hydrothermal systems and steady state chemical weathering in active mountain belts abstract hydrothermal systems are a common feature of active collisional orogens these systems can have a profound effect on the sr fluxes and sr isotopic composition of riverine waters through the direct input of sr from hot springs and groundwaters and the chemical weathering of hydrothermal calcite in an effort to quantify the role of calcite weathering we present an analytical model that examines the relationship between rock uplift and steady state chemical weathering of granites and greywackes that contain trace amounts we compare model results with sr fluxes and isotopic composition of riverine waters from the southern alps of new zealand an area that is frequently used as an example of a steady state collisional orogen as our model predicts roughly 50 of sr flux is from the weathering of calcite in the areas of highest uplift along the west flank of the southern alps this proportion decreases substantially

weathering model for the quantification of atmospheric oxygen evolution during the paleoproterozoic abstract a weathering model has been developed to quantify atmospheric oxygen evolution during the paleoproterozoic the weathering model calculates the concentrations of fe2 dissolved from fe2 bearing primary minerals and oxidized fe3 out of the dissolved fe2 at a given partial pressure of atmospheric oxygen p o 2 during weathering and establishes the relationships between p o 2 and where is the ratio of oxidized and then precipitated fe3 out of the fe2 dissolved from primary minerals to the dissolved fe2 in a whole weathering profile the weathering model considers controlling factors of the redistribution of fe during weathering that is the dissolution rate of fe2 bearing primary minerals the oxidation rate of fe2 and the groundwater flow rate the validity of the model was confirmed by applying the model to the experimental data of olivine dissolution carried out under low o2 conditions the sensitivity analysis of the model has revealed that the formation time of weathering the mineral dissolution rate and the diffusion of o2 into a weathering profile have no or slight influence on resulting in 0 0 and 0 3 changes in log p o 2 caused by four orders of magnitude change of the formation time more than 10 orders change of the mineral dissolution rate and assumed change of the o2 diffusion respectively on the other hand the temperature the ph and the groundwater flow rate have moderate to large effects on 0 6 1 4 and 1 5 changes in log p o 2 for changes of 5 c in temperature 0 5 in ph and one order of magnitude in groundwater flow rate respectively using possible surface temperature ph and groundwater flow rate estimated from the literature we calculated the p o 2 relationships which were then applied to the values of paleosols fossil weathering profiles formed between 2 5 and 1 8 ga taking account of the constraints given by the records of mass independent fractionation in sulfur isotopes and other geological proxies i e 10 6 atm at 2 32 ga and 10 3 atm at 2 0 ga our model implies that the p o 2 levels were 10 9 atm at 2 46 ga 10 4 5 10 2 atm at 2 25 2 0 ga and 10 2 atm at 1 85 ga the present weathering model can constrain p o 2 levels during the possible paleoproterozoic hot periods but not those during the glacial periods when temperature was

stable carbon isotope signatures preserved in authigenic gibbsite from a forested granitic regolith panola mt georgia usa six samples selected from a weathering profile developed on a granite in the panola mountain research watershed in the georgia piedmont were studied for their stable carbon isotopic properties the purpose was to understand the relationship between the stable carbon isotopic composition of the organic matter pool and the preservation of carbon in the authigenic soil minerals the method for yielding carbon from authigenic phases is based on that of yapp and

the missing silica sink revisiting the marine sedimentary si cycle using cosmogenic 32si burial of biogenic silica bsitotal in high sedimentation rate continental margins remains highly uncertain cosmogenic 32si t1 2 140 years can be used to trace the fates of bsitotal postdeposition including as opal bsiopal and diagenetically altered opal bsialtered the latter dominantly authigenic clay bsiclay to determine the magnitude and form of bsitotal storage in coastal sediments conventional operational leaches targeting bsiopal and bsialtered including bsiclay were modified for large scale samples necessary for measurement of 32si the 32si activity was used to estimate total biogenic silica burial bsitotal bsiopal bsialtered in several depositional settings gulf of papua gulf of mexico long island sound and in the previously studied amazon guianas deltaic system in subtropical and temperate regions 32si was detected in both traditional biogenic silica leaches bsiopal and residual authigenic clays traditional bsiopal and modified operational leaches designed to target the most reactive authigenic silicates bsialtered consistently underestimate authigenic clay formation bsiclay and thus the magnitude of bsitotal burial in temperate coastal zones and subtropical deltas by 2 4 fold in tropical deltas 32si activities in the residual fraction after removal of bsiopal demonstrate rapid and almost complete alteration of initial bsiopal to new forms most likely bsiclay globally 4 5 4 9 tmol yr si may be trapped in marine nearshore deposits as rapidly formed clay bsiclay 100 of the missing silica sink in the marine silica budget

mobility of major minor and some redox sensitive trace elements and rare earth elements during weathering of four granitoids in central portugal abstract element mobility was studied in four different granitoids in central portugal samples of fresh and weathered rock parts were collected from each type of granitoid an increase in the degree of weathering is accompanied by reductions in na 2 o cao and sio 2 plagioclase p 2 o 5 apatite and in most cases also by reduction in k 2 o biotite potash feldspar losses as well as gains are observed for mgo relative changes in the al 2 o 3 contents are attributed to physical transport or accumulation of fine weathering products mass balance calculations indicate that kaolinite and in some cases also gibbsite are the dominant weathering products this is in agreement with x ray diffraction analyses manganese is found to decrease but not fe there is a high correlation between v and fe this is preserved during weathering there were both increases and decreases in the trace elements cr as and sb u had become slightly enriched in the weathered parts no systematic trends in ree behaviour were observed differences in the behaviour of these elements and in their ratios can be explained by a combination of factors such as differential dissolution of the host minerals redox conditions and redox kinetics complexation by organic and inorganic ligands and sorption the interpretation of the results is complicated by apparent inhomogeneities in the granites on the mesoscale of an outcrop

deep weathering through time in central and northwestern europe problems of dating and interpretation of geological record abstract upland and shield areas of central and northwestern europe are characterised by an abundance of relict weathering mantles saprolites these saprolites if accurately dated and interpreted may serve as an important complementary source of information about long term environmental history in this paper methods used to establish ages of weathering mantles are reviewed such as stratigraphic and morphostratigraphic dating clay mineral and stable isotope analysis k ar and cosmogenic isotope dating particularly with reference to european examples the record of deep weathering in the mesozoic and cainozoic is examined to explain the peculiarities of the evidence and controls on the changing style of weathering through time weathering has been a continuous process through time but general and local geological conditions have resulted in different ages of preserved mantles an apparent trend from an earlier kaolinitic ferrallitic style of weathering in the mesozoic and early tertiary towards a grussic style by the end of the cainozoic does not only reflect climate change but it is also broadly consistent with tectonic geomorphic history and related changes in land surface stability miocene and plio pleistocene saprolites in particular show that in different geomorphological and lithological circumstances different types of weathering mantles could have evolved

weathering profiles and clay mineralogical developments bornholm denmark abstract saprock saprolite associations were studied by field and laboratory methods optical microscopy x ray powder diffraction scanning electron microscopy electron microprobe in order to describe regolith development in the crystalline rocks of the nygard kaolin pit bornholm denmark the clay sequences and stages of porosity development are similar to those observed for reservoir rocks from the utsira high riber et al 2016 the weathering of the parent granite began before the end of the mesozoic two stages of syn pre burial alteration followed by diagenesis during burial and then post uplift weathering have been recognized in stage plagioclase and some biotite biotite vermiculite kaolinite reacted to form elongate booklets of highly ordered kaolinite or smaller blocky pseudohexagonal crystals stage ii represented more extreme weathering developed along local fracture systems the higher potential for fluid flow in the fractures caused highly ordered kaolinite to alter to halloysitic poorly ordered kaolinite plagioclase biotite and k feldspar continued to interact with formation water and formed additional quantities of secondary clay minerals as a consequence of inter intra and trans granular cracks the original rock fabric deteriorated and porosity increased during later burial diagenetic siderite crystals filled voids and chlorite formed at the expense of kaolinite after re exposure calcite precipitated in localized zones smectite formed on a broader scale wherever high ionic strength groundwaters were present a mineralogical key to predicting where high porosity and permeability zones occur is the recognition of halloysitic poorly ordered kaolinite highly ordered kaolinite is abundant but it is ubiquitous siderite chlorite and smectite adversely affect permeability riber l dypvik h sorlie r and ferrell r 2016 clay minerals in deeply buried paleoregolith profiles norwegian north sea clays clay miner doi 10 1346 ccmn 2016 064036

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

mixed carbonate siliciclastic record on the north african margin malta coupling of weathering processes and mid miocene climate we investigated rock outcrops spanning the middle miocene global climate cooling step on the maltese islands in order to reconstruct continental weathering rates and terrigenous fluxes as well as to explore the coupling between these later regional climate and carbonate accumulations sedimentation at this location was dominated during the oligocene and early miocene by a transitional platform to slope carbonates but progressively switched to a clay rich carbonate slope system in the middle miocene around 13 ma an abrupt change toward clay dominated marls occurred and marl deposition persisted until the tortonian ca 12 ma when a shallow water carbonate ramp was reestablished clay mineralogy and bulk rock oxygen isotope analyses suggest that the deposition of the blue clay formation was mainly caused by global climate change and related change in the rate of continental weathering a significant negative correlation r 2 0 65 exists between the carbonate content and the 1 8 o record this combined with the variation of mass accumulation rate of terrigenous material suggests that shorter term periods of globally cooler climate mi events were associated with higher rates of accumulation in continental derived material since during the miocene malta was attached to the north african margin we propose that the observed trends were due to a regional increase in rainfall during cooler periods which consequently increased continental weathering and runoff we further suggest that this pattern was linked to the perturbation of atmospheric fronts due to an increased thermal gradient during the miocene thus regional increase in rainfall might have been linked to the northward migration of the intertropical convergence zone itcz

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

rare earth elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

paleoenvironmental reconstruction from chemical and isotopic compositions of permo pennsylvanian pedogenic minerals mineralogical and chemical analysis of late pennsylvanian and early permian paleosols from the eastern shelf of the midland basin north central texas usa are used to test hypothesized climate change in late paleozoic western equatorial pangea previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models the 0 2 m size phyllosilicate fraction in the studied paleosols exhibits down profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin a stratigraphic trend from kaolinite dominated profiles in upper pennsylvanian paleosols to profiles dominated by smectite and hydroxy interlayered 2 1 phyllosilicates in lower permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest pennsylvanian followed by a more gradual decrease in leaching throughout the early permian the chemical composition cation ratios and exchange capacity of these phyllosilicates further corroborates this shift toward less intensive leaching presumably in response to climate change from humid to progressively more arid conditions the phyllosilicates in the 0 2 m size fraction and contemporaneous pedogenic calcites from the permo pennsylvanian paleosols exhibit a long term stratigraphic increase in their 18o values of as much as 3 2 and 5 2 respectively this long term trend is consistent with a transition throughout the latest pennsylvanian through early permian toward progressively more evaporatively enriched soil waters superimposed on the long term trend is an apparent rapid enrichment 1 5 to 2 in phyllosilicate 18o values immediately above the pennsylvanian permian boundary observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs this is attributed to a minor detrital component in the pedogenic clay dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation inferred 18o compositions of late paleozoic meteoric water 2 to 4 are compatible with less intensive soil leaching under conditions of increasing aridity possibly coupled with a shift in local precipitation from a continental source to a marine source

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

temporal variations in the fractionation of the rare earth elements in a boreal river the role of colloidal particles rare earth element ree data from weekly sampling of the filtered 0 45 m and suspended particulate phase during 18 months in the kalix river northern sweden are presented together with data on colloidal particles and the solution fraction 3 kda the filtered ree concentration show large seasonal and temporal variations in the river lanthanum varied between approximately 300 and 2100 pm high ree concentration in the filter passing fraction is related to increased water discharge and there is a strong correlation between the ree concentration organic carbon al and fe physical erosion of detrital particles plays a minor role for the yearly transport of particulate ree in this boreal river system the suspended particulate fraction which is dominated by non detrital fractions accounted for only 35 of the yearly total transport of la in the river approximately 10 of the ree were transported in detrital particles during winter at spring flood in may about 30 of the lree and up to 60 of the hree where hosted in detrital particles ultrafiltration of river water during spring flood shows that colloidal particles dominate the transport of filter passing ree less than 5 of the filtered ree are found in the fraction smaller than 3 kda the colloidal fraction shows a flat to slightly lree enriched pattern whereas the solution fraction 3 kda show an hree enriched pattern compared with till in the catchment suspended particles show a lree enriched pattern data indicate that the ree are associated with two phases in the colloidal and particulate fraction an organic rich phase with associated al fe and an fe rich fe oxyhydroxide inorganic phase the ce anomaly in the suspended particulate fraction in the river shows systematic variations and can be used to interpret fractionation processes of the ree during weathering and transport there was no anomaly at maximum spring flood but during the ice covered period the anomaly became more and more negative the temporal and seasonal variations of the ce anomaly in the suspended particulate phase reflect transport of ree c al fe enriched colloids from the upper section of the till and or from mires to the river at storm events

clay minerals in the sediments of lake baikal a useful climate proxy lake baikal in south central siberia has been the focus of an international effort the baikal drilling project bdp to obtain continuous long cores upwards of 100 m from this unique rift valley lake and to interpret the paleoclimatic history from various proxy data as part of this effort the clay minerals were examined by two research teams a consistent clay mineral assemblage containing illite inter stratified illite smectite chlorite and kaolinite as the major minerals characterizes much of the modern sediments the relative abundance of these minerals changes with depth in both short piston cores from various parts of the lake and in 100 m long cores taken from the distal toe of the selenga delta bdp 93 independent analyses of the abun dance changes and correlation with other data from the cores show that the clays are responding to two influences 1 climatic fluctua tions particularly in the upper 40 m of the sedimentary record which show the relative amount of illite smectite and sometimes kaolinite increasing during warmer climate episodes and 2 source area chang es which are most evident below 40 m in the bdp 93 cores and mark a shift from an eastern buguldeika river to a western selenga river source the clay mineral based climate fluctuations are correlative with the marine oxygen isotope record through stage 7 and provide a relatively simple and cost effective tool for gaining insight into the pa leoclimate of this interior continental site

geochemical mass balances and weathering rates in forested watersheds of the southern blue ridge ii effects of botanical uptake terms abstract geochemical mass balance methods are commonly used in small watershed studies to estimate rates of primary mineral weathering and soil formation and the contribution of these processes to cation budgets nutrient cycling and landscape susceptibility to acid deposition many researchers employ the balance sheet approach a system of simultaneous linear equations with constant coefficients which represent the steady state behavior of the modelled system most workers also assume that the steady state assumption for the entire system means that botanical factors can be ignored in other words that there is no net elemental transfer between biomass and inorganic compartments of the system however the widely invoked assumption that biomass is at steady state is mathematically a second explicit assumption not a built in mathematical consequence of the assumption of overall steady state the common assumption that the biomass is necessarily at steady state in a steady state system ignores the possibility of uptake of elements into the forest biomass to quantify the implications of the separate mathematical assumptions weathering rates for seven forested watersheds in the southern blue ridge mountains are calculated twice once allowing for net element exchange with biomass and once assuming no net exchange with biomass our calculations show that misunderstanding the mathematical constraints which are built into the most widely used geochemical mass balance equations commonly causes errors underestimates of up to a factor of 4 in the calculated rates of mineral weathering and soil formation this problem is most pronounced for minerals which contain major nutrient elements and for rates calculated from mass balances of those nutrient elements

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

mass balance modeling of mineral weathering rates and co2 consumption in the forested metabasaltic hauver branch watershed catoctin mountain maryland usa mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested metabasaltic hauver branch watershed in north central maryland usa previous studies of hauver branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering including biomass more equations in the mass balance matrix were added using existing mineralogic information the stoichiometry of a deciduous biomass term was determined using multi year weekly to biweekly stream water chemistry for a nearby watershed which drains relatively unreactive quartzite bedrock at hauver branch calcite hosts 38 mol of the calcium ion ca2 contained in weathering minerals but its weathering provides 90 of the stream water ca2 this occurs in a landscape with a regolith residence time of more than several ka kiloannum previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream ca2 na ratios the relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone of the carbon dioxide co2 consumed by mineral weathering calcite is responsible for approximately 27 with the silicate weathering consumption rate far exceeding that of the global average the chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles and therefore climate on geological timescales based on carbon balance calculations atmospheric derived sulfuric acid is responsible for approximately 22 of the mineral weathering occurring in the watershed our results suggest that rising air temperatures driven by global warming and resulting in higher precipitation will cause the rate of chemical weathering in the hauver branch watershed to increase until a threshold temperature is reached beyond the threshold temperature increased recharge would produce a shallower groundwater table and reduced chemical weathering rates copyright 2013 john wiley sons ltd

mineral weathering and elemental transport during hillslope evolution at the susquehanna shale hills critical zone observatory located in the uplands of the valley and ridge physiographic province of pennsylvania the susquehanna shale hills critical zone observatory ssho is a tectonically quiescent first order catchment developed on shales of the silurian rose hill formation we used soil cores augered at the highest point of the watershed and along a subsurface water flowline on a planar hillslope to investigate mineral transformations and physical chemical weathering fluxes about 25 m of bedrock was also drilled to estimate parent composition depletion of carbonate at tens of meters of depth in bedrock may delineate a deep carbonate weathering front overlying this extending from 6 m below the bedrock soil interface up into the soil is the feldspar dissolution front in the soils depletion profiles for k mg si fe and al relative to the bedrock define the illite and chlorite reaction fronts when combined with a cosmogenic nuclide derived erosion rate on watershed sediments these depletion profiles are consistent with dissolution rates that are several orders of magnitudes slower for chlorite 1 5 10 17 mol m 2 s 1 and illite 2 9 10 17 mol m 2 s 1 than observed in the laboratory mineral reactions result in formation of vermiculite hydroxy interlayered vermiculite and minor kaolinite during weathering exchangeable divalent cations are replaced by al as soil ph decreases the losses of mg and k in the soils occur largely as solute fluxes in contrast losses of al and fe are mostly as downslope transport of fine particles physical erosion of bulk soils also occurs results from a steady state model demonstrate that physical erosion accounts for about half of the total denudation at the ridgetop and midslope positions chemical weathering losses of mg na and k are higher in the upslope positions likely because of the higher degree of chemical undersaturation in porewaters chemical weathering slows down in the valley floor and al and si even show net accumulation the simplest model for the hillslope that is consistent with all observations is a steady state clay weathering limited system where soil production rates decrease with increasing soil thickness

effects of physical erosion on chemical denudation rates a numerical modeling study of soil mantled hillslopes article i nfo many biogeochemical and earth surface processes depend critically on chemical weathering the immediate products of chemical weathering are present as solutes and secondary minerals in groundwater soils and streams and form the nutritional foundation for terrestrial biogeochemistry chemical weathering also contributes to physical erosion by weakening bedrock and producing easily erodible regolith and as the primary long term sink for atmospheric co2 it modulates earth s long term climate via the greenhouse effect long term chemical denudation rates on soil mantled hillslopes can be estimated from cosmogenic radionuclide crn concentrations in soil borne quartz and the enrichment of a chemically inert tracer in soil relative to its parent bedrock a technique that inherently assumes steady physical erosion over the timescale of crn accumulation we present a numerical model that computes changes in soil mineralogy and crn concentrations under time varying physical erosion rates and we use this model to assess the accuracy of the crn based technique for estimating chemical denudation rates in non steady conditions our modeling results suggest that crn based estimates of chemical denudation rates closely resemble actual chemical denudation rates averaged over the timescale of crn accumulation even during large amplitude and long period oscillations in physical erosion rates for example this model predicts that when physical erosion rates fluctuate sinusoidally by 50 of their mean over any period in time crn based estimates of chemical denudation rates should differ from actual chemical denudation rates by less than 15 our model also implies that chemical denudation rates should approach zero both when physical erosion rates approach zero because soluble minerals become depleted in the soil and when physical erosion rates approach the maximum soil production rate because soil thickness approaches zero modeled chemical denudation rates thus reach a maximum at intermediate physical erosion rates if this relationship holds in nature it implies that in rapidly eroding regions further increases in physical erosion rates e g due to increases in tectonic uplift rates may not necessarily lead to faster chemical denudation on soil mantled hillslopes published by elsevier b v

monazite chemical weathering rare earth element behavior and paleoglaciohydrology since the last glacial maximum for the loch vale watershed colorado usa rare earth element ree release from weathering of accessory monazite ree po4 since the last glacial maximum at 18 1 ka was investigated in sediment recovered from an outlet lake within the glaciated loch vale watershed colorado usa labile rees in the sediments reveal monazite weathering increased during the younger dryas chronozone ydc 13 2 to 11 1 ka when alpine glaciers advanced as climate cooled and bedrock comminution increased monazite dissolution peaked at approximately the pleistocene holocene transition 10 5 ka during the holocene ree concentrations decline reflecting a reduction in monazite weathering the ree cerium ce may occur as trivalent or tetravalent cations and the ce anomaly ce n ce n in sediment permits interpretations of paleoredox conditions the ce n ce n decreases from 18 1 ka to the pleistocene holocene boundary initially oxidizing conditions within the watershed increased because of enlargement of the proglacial area as the ice retreated at the onset of the ydc oxidation further escalated in response to enhanced chemical weathering associated with glacial advance a more stable holocene climate and landscape resulted in relatively small changes in ce n ce n values slightly decreasing ce n ce n values over the last several hundred years are consistent with present day stream water values and may reflect the onset of present day hydrobiogeochemical conditions

natural weathering mechanisms of almandine garnet the weathering of almandine garnet in the oxidized vadose zone of saprolite near otto north carolina begins at grain boundaries and along fractures traversing the garnet grains radially oriented fibrous intergrowths of gibbsite and goethite form layers of uniform thickness which grow by centripetal replacement as weathering proceeds the contact between the garnet surface and the layer of weathering products is sharp and smooth and garnet corners are rounded large well defined etch pits are absent on the underlying garnet surface these observations suggest that diffusion transport of reactants and or products through the gibbsite goethite layer is the rate limiting step in the weathering of almandine garnet in the oxidizing environment of the saprolite in soils overlying the saprolite garnet surfaces are directly exposed to weathering solutions without the intervening surface layer such unprotected grains in soils and stream sediments exhibit numerous large well developed etch pits surface reaction control rather than transport control prevails during weathering of almandine garnet in the absence of protective surface layers of weathering products biochemical or biological processes in the soil apparently prevent the gibbsite goethite layer from forming or persisting soil solutions can therefore react directly with the garnet surface rather than requiring reactants or products to diffuse through the gibbsite goethite coating as in the saprolite the mechanism and rate limiting step of almandine garnet weathering is apparently strongly dependent on the chemical environment in which weathering occurs

climatic impact on isovolumetric weathering of a coarse grained schist in the northern piedmont province of the central atlantic states the possible impact of periglacial climates on the rate of chemical weathering of a coarse grained plagioclase muscovite quartz schist has been determined for a small watershed near baltimore maryland the isovolumetric chemical weathering model formulated from the geochemical mass balance study of the watershed shows that the weathering front advances at a velocity of 9 1 m m y if the modern environmental parameters remain the same back through time however recent surficial geological mapping demonstrates that periglacial climates have impacted the area such an impact significantly affects two key chemical weathering parameters the concentration of co2 in the soil and groundwater moving past the weathering front depending upon the assumptions used in the model the rate of saprolitization varies from 2 2 to 5 3 m m y the possible impact of periglacial processes suggested by the chemical weathering rates indicates a need to reconsider theories of landscape evolution as they apply to the northern piedmont province of the mid atlantic states i suggest that from the late miocene to the present that the major rivers have become incised in their present locations this incision has enhanced groundwater circulation and chemical weathering such that crystalline rocks beneath interfluvial areas remain mantled by saprolite and the saprolite mantle has been partially stripped as periglacial conditions alternate with humid temperate conditions

apparent gibbsite growth ages for regolith in the georgia piedmont abstract carbon bound in gibbsite collected from a residual weathering profile developed on a paleozoic granite in the georgia piedmont was examined for its 14 c content and found to be geologically young the study site located at the panola mountain research watershed has developed a granite saprolite soil regolith in which 14 c gibbsite model ages deep within the profile c horizon average about 8000 years near the surface a and b horizon 14 c gibbsite model ages range from 2100 to 4200 years quartz has acquired 26 al and 10 be inventories suggesting a near surface residence time of at least 90 000 years this age disparity supports the notion that secondary minerals undergo significant recrystallization as weathering fronts propagate into the landscape combining the results of 14 c 26 al and 10 be analyses offers the potential to assess differential rates of chemical weathering and continental denudation to understand better the links between rates of silicate rock weathering climate and soil residence times

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

dating constituent formation in soils to determine rates of soil processes a review abstract rates of soil processes are poorly known one approach to determine them could be through the radiogenic isotopic dating of soil constituents such methods have been recently used to date minerals in soils and weathering profiles thanks to the development of high resolution techniques such as 40ar 39ar u series of micro drilled samples u series by laser ablation and u th he and to the development of suitable methodology expanding application of the techniques to a variety of supergene minerals e g fe and mn oxihydroxides carbonates etc in this paper we identify i the main soil constituents that can be dated through these isotopic methods that are mainly fe oxides mn oxides pedogenic carbonates and organic matter ii the main pedogenic processes that leads to their formation in soils and iii the different soil settings that allow transforming soil constituent ages into rates of soil processes namely growth bands transformation fronts and chronosequences

rates and time scales of clay mineral formation by weathering in saprolitic regoliths of the southern appalachians from geochemical mass balance rates of clay formation in three watersheds located at the coweeta hydrologic laboratory western north carolina have been determined from solute flux based mass balance methods a system of mass balance equations with enough equations and unknowns to allow calculation of secondary mineral formation rates as well as the more commonly determined primary mineral dissolution rates was achieved by including rare earth elements ree in the mass balance rates of clay mineral formation determined by mass balance methods have been used to calculate the time needed for a 5 50 g kg 1 change in relative clay abundance in the saprolite at coweeta this corresponds to the response time of the clay mineral to for example a change in climate the 5 change in relative clay abundance is the smallest change that can generally be detected using x ray diffraction xrd response times range from tens of thousands to hundreds of thousands of years extrapolating the coweeta clay formation rates to other southern appalachian regoliths the time required to form measured clay abundances production times in eastern blue ridge and inner piedmont regolith have been calculated the production times of clay mineral assemblages range from 2 k y to 2 m y with mean values ranging from 50 k y to 1 m y the results of this study are consistent with the arguments of thiry 2000 1 that the best resolution of the paleoclimatic record in marine clay rich sediments and mudrocks is 1 or 2 m y 1 ref 107

rare earth elements and sr and nd isotopic compositions of dissolved and suspended loads from small river systems in the vosges mountains france the river rhine and groundwater abstract the aim of this study is to characterize the evolution of the rare earth elements ree in non mature streams from small catchment areas in the vosges mountains downstream to more mature plain rivers including the river rhine the dissolved load ree distribution patterns of the low ph vosges streams are very different from those of high ph plain rivers indicating that different physico chemical parameters control ree transport in these different water systems the plain rivers and groundwater show similar ree distribution patterns with a strong negative ce anomaly and heavy rare earth element hree enrichment in addition the river rhine has a positive gd anomaly which is of anthropogenic origin similar to the world s major rivers the light rare earth element lree enrichment in the plain rivers is mainly ph controlled their sm nd and 143 nd 144 nd isotope ratios are close to average continental crust values this is not the case for the less evolved non mature and low ph vosges streams their high sm nd and 143 nd 144 nd ratios but low 87 sr 86 sr ratios suggest that chemical alteration of accessory middle rare earth element mree enriched minerals such as apatites from rocks in the catchment area control the ree abundances of these waters a comparison of the dissolved load ree distribution patterns with those of the principal lithologies in the corresponding drainage basins illustrates that especially the eu anomalies of the vosges streamlets are strongly lithology dependent leaching experiments indicate that the suspended load is isotopically very inhomogeneous the ree distribution patterns of the suspended load leachates have no similarities with those of the corresponding dissolved load indicating that the leachable reservoir not only contains adsorbed ree but also ree from leachable mineral phases their 143 nd 144 nd sm nd and 87 sr 86 sr ratios support this suggestion being always higher and lower respectively than those of their corresponding dissolved loads they rather point to the presence of relic primary apatite in the leachable portion of the suspended load the flat paas normalized ree distribution patterns the high 87 sr 86 sr and low 143 nd 144 nd isotopic ratios of the corresponding residues suggest secondary silicate phases such as clay minerals in the residual phase of the suspended load leachates and corresponding residual phases define alignments in the sm nd isochron diagram whose slopes define ages ranging between 200 and 390 ma indicating that the mineral phases in the suspended load retain some memory of their primary precursor minerals in the hercynian granitic source rocks

ree fractionation during granite weathering and removal by waters and suspended loads sr and nd isotopic evidence very few studies deal with ree rare earth element mobility within the system soil soil solution streamwater in this article we try to characterize the fractionation and the migration of the ree in a granite derived soil system located in a small catchment of the vosges mountains icp ms and tims measurements were performed on both solid samples fresh granite soil and suspended load of the stream and waters soil solutions springwater and streamwater to determine their respective ree concentrations and sr and nd isotopic compositions the paas normalized ree pattern of the bedrock is characterized by a strong depletion in hree heavy ree and a negative eu anomaly 0 46 similarly the granite normalized ree distribution patterns of the soil samples show hree depletions that become more important with decreasing depth the correlative behavior between p2o5 th and ree with depth indicates that besides apatite other phosphate minerals such as monazite are the most important phases controlling the th and ree budget in the soil profile on the other hand at greater depth zircon seems to be another important mineral phase controlling especially the hree enrichment as shown by the positive relationship between zr content and the yb ho ratio different grain size fractions show similar ree distribution patterns and are only weakly fractionated compared with bulk soil sample however the finest fraction 0 20 m is more enriched in sr and ree suggesting a stronger concentration of ree carrying minerals in this fraction the suspended and dissolved load of the stream show as a whole an enrichment in hree if compared with the granite or with the different soil samples however compared with the uppermost soil samples the suspended load is significantly more enriched in hree its ree distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the fresh granite thus most probably the ree of the suspended load originated from a source with ree characteristics found in the deep soil horizons this source might have been situated in the uppermost soil profile which is actually ree depleted the weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite the sr isotope data indicate that the suspended load originates from the finest soil fraction the sr and nd isotopic data of the suspended load suggest that it contains up to 3 sr and nd from apatite and up to 97 from feldspar most of the sr and nd in the waters originate from apatite leaching or dissolution

long term average mineral weathering rates from watershed geochemical mass balance methods using mineral modal abundances to solve more equations in more unknowns abstract the number of phases for which weathering rates can be determined by watershed geochemical mass balance is limited by the number of equations that can be constructed from elemental flux losses from the watershed and mineral stoichiometries mass balance studies of watershed weathering rates routinely use the flux losses of the six major cations sio 2 al na k mg and ca analyses of these species in water are common but following matrix algebraic methods limits the number of weathering rates that can be calculated to six for the brubaker run watershed located in the northern piedmont physiographic province of pennsylvania usa long term 10 3 10 6 year watershed chemical flux losses have been determined using 10 be derived total denudation rates and zirconium normalized total chemical concentrations from bedrock and soils chemical flux losses calculated from solid phase data have three advantages they 1 permit generation of a relatively large number of equations because both major and trace analyses are included 2 eliminate the need for many years of regular e g weekly sampling and chemical analyses of stream water and atmospheric precipitation and measurement of hydrologic parameters i e precipitation stream discharge etc and 3 long term weathering rate calculations need not address biomass for brubaker run eight minerals are involved in weathering the five primary minerals are ree rich epidote ankerite almandine spessartine garnet muscovite chlorite and the three secondary products are weathered muscovite kaolinite and gibbsite the long term average weathering rates of these minerals were calculated using the six major cations and two trace elements selected from rb sr ba la pr nd sm gd and dy despite having the eight equations needed geochemically reasonable weathering rates e g positive primary mineral rates that reflect destruction could not be achieved regardless of the two trace elements used in the mass balance calculations for brubaker run this is primarily attributable to the natural heterogeneity of the trace element concentrations within the host mineral grains with trace element stoichiometries in some minerals varying by as much as an order of magnitude because the trace elements are hosted by a relatively small number of minerals the computed weathering rates of other minerals become very sensitive to small variations in trace cation stoichiometry ree rich epidote garnet and ankerite within the brubaker run watershed together host nearly all of the ca in the bedrock and completely dissolve at or near the weathering front consequently approximately all of the ca in bedrock is lost from the regolith in bedrock the mole percentages of ca hosted by ree rich epidote garnet and ankerite are 49 mol 4 mol and 43 mol respectively and are determined by the modal abundance of the mineral in the bedrock and its ca stoichiometry the weathering rates of ree rich epidote garnet and ankerite can be determined by distributing to each mineral that fraction of the total watershed ca flux loss for which it is responsible based on its mole percent ca in bedrock by using a base cation that is completely lost from the regolith and knowing the mole percentage of that element in the mineral s undergoing weathering additional equations may be added to the mass balance matrix we term this technique the flux distribution method the flux distribution method eliminates the need for additional equations established using trace elements based on the mineral weathering rates for the brubaker run watershed determined using the flux distribution method the rates at which the weathering front penetrated the bedrock the saprolitization rate are 4 5 m myr 1 and 6 5 m myr 1 for chlorite and muscovite respectively these measured long term average saprolitization rates compare very favorably with published theoretical values for the nearby northern maryland piedmont which range from 2 2 to 5 3 m myr 1

mineral specific chemical weathering rates over millennial timescales measurements at rio icacos puerto rico abstract mineral weathering plays a prominent role in many biogeochemical and geomorphological processes it supplies nutrients to soils and streams accelerates physical erosion by weakening bedrock and producing easily erodible soil and modulates earth s long term climate by drawing down atmospheric carbon dioxide we calculate mineral specific chemical weathering rates at two field sites in the rio icacos catchment puerto rico by combining new mineral abundance measurements from quantitative powder x ray diffraction xrd with existing measurements of i soil production rates from cosmogenic nuclides ii chemical alteration of the regolith from x ray fluorescence xrf and iii dust deposition rates the central purpose of this paper is to show that combining measurements of cosmogenic nuclides with xrf based geochemistry and xrd based mineralogy can in favorable cases provide weathering rates of abundant soluble mineral phases in actively eroding terrain to an accuracy of better than 20 of the mean even in places with high dust deposition rates mineral weathering at our two field sites is dominated by plagioclase at rates of 3274 575 mol ha 1 yr 1 and 3077 541 mol ha 1 yr 1 followed by hornblende at 187 71 mol ha 1 yr 1 and 308 93 mol ha 1 yr 1 within the uncertainty of our data all weathering of these primary minerals occurs below the saprolite soil interface our measurements imply that kaolinite production in saprolite is roughly 1 3 times faster than kaolinite weathering in the soil our results are the first to show that field measurements of cosmogenic nuclides xrf xrd and dust fluxes can be combined within the geochemical mass balance method to quantify long term mineral weathering rates even in locations with high dust deposition rates this implies that the mass balance method can be a valuable tool for quantifying the effects of climate vegetation tectonics and other factors on weathering rates of individual mineral phases

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

geochemical and mineralogical behavior of ree th and u in the akongo lateritic profile sw cameroon abstract the ree u th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite akongo sw cameroon mass balance calculations have been done 1 in the syenite to determine the most important ree u th bearing minerals and 2 in the soil profile to understand the movement of these elements thorium has been used as an immobile element for these calculations the weathering of accessory minerals rich in ree and th of the syenite allanite apatite titanite and epidote has been especially studied in the saprolite several ree th secondary minerals florencite rhabdophane cerianite and thorianite important to explain the fractionation of ree in supergene environments have been found

the influence of climate and topography on rock fragment abundance in modern fluival sands of the southern blue ridge mountains north carolina chemical weathering influences the detrital composition of sand size sediment derived from source areas subject to different amounts of precipitation in the coweeta basin north carolina of the grain types studied rock fragments are most sensitive to chemical degradation therefore their abundance is the best indicator of cumulative weathering effects destruction of sand size rock fragments by chemical weathering is a function of both the intensity and duration of chemical weathering experienced by grains in regoliths of the source area in the coweeta basin the intensity of chemical weathering is directly related to the climate via effective precipitation in individual subbasins whereas the duration of chemical weathering is inversely related to the relief ratio of the watershed therefore soils in watersheds with low relief ratios and high discharge per unit area experience the most extensive chemical weathering and sediments derived from these watersheds contain the lowest percentage of rock fragments the effects of climate alone cannot explain the systematic variation of rock fragment abundance in sediments from the coweeta basin the compositional imprint left on these sediments by chemical weathering is a function of both climate and topographic slope in the sediment source area

carboniferous permian facies and tectono stratigraphic successions of the glacially influenced and rifted carnarvon basin western australia abstract the carnarvon basin of western australia is a rift basin that contains a thick up to 5 km succession of late carboniferous early permian glacially influenced marine sedimentary strata these rocks accumulated in near polar paleolatitudes along the uplifted and glaciated margin of the west australian shield pilbara craton three stratigraphic successions i ii iii can be recognised each characterised by distinct facies associations that record different stages in the tectonic evolution of the basin and associated changes in the rate of basin subsidence and sediment accommodation a lowermost succession i comprises rapidly deposited 30 m ma glacially influenced marine strata lyons group containing palynomorphs of westphalian tastubian early sakmarian and possibly older age strata are dominated by subaqueously deposited sediment gravity flow facies succession ii is composed of richly fossiliferous cool water shales callythara and cordalia formations that record much reduced sedimentation rates 2 m ma in turn shales are overlain by an uppermost succession iii of shallow marine wave and storm influenced sandstone moogooloo sandstone comparison with other rift basin fills indicates that succession i likely records initial basin infilling where abundant coarse debris was produced by faulting and glaciation of the adjacent pilbara craton shales of succession ii mark a phase of sediment underfilling characterized by rapid tectonic subsidence an increase in relative sea level and reduced sediment supply shallow water sandstone facies of succession iii record a late stage in the tectonic cycle when subsidence rates had decreased and sediment supply outpaced accommodation such successions where found in other late paleozoic basins are widely interpreted in terms of glacioeustatically driven changes in sea level resulting from deglaciation events across gondwana instead the three successions within the carnarvon basin are argued to reflect a dominantly tectonic control on sedimentation and preservation

estimates of atmospheric o 2 in the paleoproterozoic from paleosols abstract a weathering model was developed to constrain the partial pressure of atmospheric o 2 p o 2 in the paleoproterozoic from the fe records in paleosols the model describes the fe behavior in a weathering profile by dissolution precipitation of fe bearing minerals oxidation of dissolved fe ii to fe iii by oxygen and transport of dissolved fe by water flow in steady state the model calculates the ratio of the precipitated fe iii oxyhydr oxides from the dissolved fe ii to the dissolved fe ii during weathering as a function of p o 2 an advanced kinetic expression for fe ii oxidation by o 2 was introduced into the model from the literature to calculate accurate p o 2 relationships the model s validity is supported by the consistency of the calculated p o 2 relationships with those in the literature the model can calculate p o 2 for a given paleosol once a value and values of the other parameters relevant to weathering namely ph of porewater partial pressure of carbon dioxide p co 2 water flow temperature and o 2 diffusion into soil are obtained for the paleosol the above weathering relevant parameters were scrutinized for individual paleoproterozoic paleosols the values of temperature ph and p co 2 were obtained from the literature on the paleoproterozoic paleosols the parameter value of water flow was constrained for each paleosol from the mass balance of si between water and rock phases and the relationships between water saturation ratio and hydraulic conductivity the parameter value of o 2 diffusion into soil was calculated for each paleosol based on the equation for soil o 2 concentration with the o 2 transport parameters in the literature then we conducted comprehensive p o 2 calculations for individual paleoproterozoic paleosols which reflect all uncertainties in the weathering relevant parameters consequently robust estimates of p o 2 in the paleoproterozoic were obtained 10 7 1 10 5 4 atm at 2 46 ga 10 5 0 10 2 5 atm at 2 15 ga 10 5 2 10 1 7 atm at 2 08 ga and more than 10 4 6 10 2 0 atm at 1 85 ga comparison of the present p o 2 estimates to those in the literature suggests that a drastic rise of oxygen would not have occurred at 2 4 ga supporting a slightly rapid rise of oxygen at 2 4 ga and a gradual rise of oxygen in the paleoproterozoic in long term

quantification of the dry history of the martian soil inferred from in situ microscopy 1 the particle size distribution psd of a martian soil sample a useful indicator of the underlying soil formation processes has been determined using optical and atomic force microscopy data acquired by the phoenix mars lander in particular the presence and fraction of clay sized particles in the psd reflects the extent of aqueous interaction with the soil two size populations have been identified for the martian sample larger mostly rounded grains and small reddish fines notably with a very low mass proportion in the clay size range below 2 m these fines reflect the smallest scale formation processes and indicate a single method of production for the particles up to 11 m a much larger value than that expected for the aqueous interaction of clay formation this suggests the fines are predominantly the product of global aeolian weathering under very dry conditions the proportion of clay sized soils can be used to estimate that there has been much less than 5 000 years exposure to liquid water over the history of the soil from the perspective of the psd lunar regolith rather than terrestrial soil is the best analog to martian soil a globally homogenous soil with such a psd would be an unlikely habitat for the propagation of life on mars

headwater stream length dynamics across four physiographic provinces of the appalachian highlands understanding patterns of expansion contraction and disconnection of headwater stream length in diverse settings is invaluable for the effective management of water resources as well as for informing research in the hydrology ecology and biogeochemistry of temporary streams more accurate mapping of the stream network and quantitative measures of flow duration in the vast headwater regions facilitate implementation of water quality regulation and other policies to protect waterways we determined the length and connectivity of the wet stream and geomorphic channel network in three forested catchments 90 of the mean daily discharge stream network dynamics reflected geologic controls at both regional and local scales wet stream length was most variable at two valley and ridge catchments on a shale scarp slope and changed the least in the blue ridge the density and source area of flow origins differed between the crystalline and sedimentary physiographic provinces as the appalachian plateau and valley and ridge had fewer origins with much larger contributing areas than new england and the blue ridge however the length and surface connectivity of the wet stream depended on local lithology geologic structure and the distribution of surficial deposits such as boulders glacially derived material and colluival debris or sediment valley fills several proxies indicate the magnitude of stream length dynamics including bankfull channel width network connectivity the base flow index and the ratio of geomorphic channel to wet stream length consideration of geologic characteristics at multiple spatial scales is imperative for future investigations of flow intermittency in headwaters

a simple kinematic mechanism for mixing fluid parcels across a meandering jet abstract recent observations of fluid parcel pathways in the gulf stream using isopycnal rafos floats revealed a striking pattern of cross stream and vertical motion associated with meanders bower and rossby 1989 in an attempt to explain the observed pattern a two dimensional kinematic model of a meandering jet has been developed which enables examination of the relationship between streamfunction patterns and fluid parcel trajectories the streamfunction fields are displayed in a reference frame moving with the wave pattern so motions of fluid parcels relative to the jet can be seen more easily the results suggest that the observed pattern of cross stream motion results primarily from the downstream phase propagation of meanders the model successfully reproduces several of the most distinctive features of the float observations 1 entrainment of fluid into the gulf stream occurs at the leading edges of meander extrema while detrainment takes place at the trailing edges 2 exchange between the gu

reactant product textures volume relations and implications for major element mobility during natural weathering of hornblende tallulah falls formation georgia blue ridge u s a natural weathering of hornblende from the tallulah falls formation georgia u s a takes place under thoroughly leached oxidizing conditions at the earliest stage of weathering corrosion of hornblende forms denticulated terminations with only minimal porosity apparent within the partially pseudomorphic kaolin group weathering product or between it and the reactant mineral isovolumetric replacement of hornblende by kaolin group clay or precursor products implies inheritance of parent mineral silica tetrahedra by the weathering products and largely immobile behavior of si during early weathering aluminum normally considered immobile or minimally mobile during weathering must be imported into early stage weathering products more advanced weathering of hornblende forms denticulated terminations separated from the earlier formed products by a large continuous peripheral void porosity is much more conspicuous at this stage late stage ferruginous products precipitate from fe mobilized in solution dissolved fe to form the late stage goethite can be entirely derived from the parent hornblende requiring only short transport distances for aqueous fe between the source parent mineral and the location of product precipitation textural and volumetric relationships between naturally weathered hornblende and its partially pseudomorphic weathering products suggest structurally controlled immobility of much parent mineral si and considerable mobilization of al at early stages of weathering but at more advanced stages of weathering the textural and volumetric relationships are consistent with immobility of al and fe and leaching of substantial si and all base cations

solute geochemical mass balances and mineral weathering rates in small watersheds ii biomass nutrient uptake more equations in more unknowns and land use land cover effects abstract paired watersheds are used to develop a deciduous nutrient uptake stoichiometry the watersheds are those of the house rock run and the brubaker run located in the pennsylvania appalachian piedmont usa these two watersheds are nearly identical with respect to bedrock regolith climate geomorphology morphometry baseflow hydrology and type and successional stage of forest vegetation they only differ by the percentage of deciduous forest cover with house rock run having 59 and brubaker run having 76 from differences in their stream chemistries the biomass nutrient uptake stoichiometry of k1 0mg1 0ca1 4 was determined this stoichiometry applies to an aggrading deciduous biomass and differs from those previously used which were derived from net primary production npp data the difference may reflect that macronutrients in plant tissue may also originate from atmospheric inputs and or decomposing biomass although this stoichiometry may not be applied to all deciduous forest covered watersheds it is likely an improvement over a stoichiometry determined from npp data mass balance calculations of mineral weathering rates often suffer from the number of unknowns exceeding the number of equations to add equations to the mass balance matrices two methods are introduced the first method employs zr normalized bulk chemical compositions of bedrock and soil to calculate a mass transfer coefficient for chemical weathering the second approach uses chemical formulae and modal abundances of primary minerals undergoing complete dissolution during weathering both methods allow for calculation of weathering rate constraints without biomass and cation exchange influences these constraints serve as additional equations in the mass balance matrix this study finds that the watershed with the higher percentage of recently abandoned agricultural fields previously used for growing row crops has the higher chemical weathering rate the higher chemical weathering rate reflects greater runoff resulting from reduced evapotranspiration

basalt and rhyo dacite weathering and soil clay formation under subtropical climate in southern brazil abstract the mineralogy of highly weathered soils is dominated by kaolinite group clay minerals however in the highlands of southern brazil the subtropical climate mean annual temperature 15 c mean annual precipitation 1900 mm yr favored accumulation of organic matter and occurrence of 2 1 clay minerals the objective of this work was to compare the weathering of the two main rock types in the volcanic plateau in the rio grande do sul in southern brazil in order to consider soil fertility and sustainability in this intensively cropped area two weathering profiles were sampled on basalt and rhyo dacite at elevations ranging between 760 and 850 m a s l the soil minerals were analyzed by x ray diffraction chemical extractions and ftir spectroscopy weathering intensity was inferred from bulk chemical analyses and calculation of weathering indices chemical index of alteration cia weathering intensity scale wis and elemental mass balance mineralogy was dominated by kaolinite and crystalline iron and aluminum oxy hydroxides and 2 1 clay minerals the surface horizons contained hydroxyl al interlayered minerals originating from aluminization of smectite present in the saprolite under acidic conditions with the important accumulation of organic matter results of mass balance calculation showed extensive loss of all elements high 4si wis and cia with residual accumulation of fe and al oxy hydroxides the degree of weathering is higher on rhyo dacite compared to basalt although rhyo dacite rock is richer in sio2 given the importance of 2 1 clay minerals on soil properties e g sorption aggregation a better understanding of their formation and transformation according to geochemical conditions is a key issue in the management of these sub tropical soils

regolith production rates calculated with uranium series isotopes at susquehanna shale hills critical zone observatory abstract in the critical zone where rocks and life interact bedrock equilibrates to earth surface conditions transforming to regolith the factors that control the rates and mechanisms of formation of regolith defined here as material that can be augered are still not fully understood to quantify regolith formation rates on shale lithology we measured uranium series u series isotopes 238 u 234 u and 230 th in three weathering profiles along a planar hillslope at the susquehanna shale hills observatory ssho in central pennsylvania all regolith samples show significant u series disequilibrium 234 u 238 u and 230 th 238 u activity ratios range from 0 934 to 1 072 and from 0 903 to 1 096 respectively these values display depth trends that are consistent with fractionation of u series isotopes during chemical weathering and element transport i e the relative mobility decreases in the order 234 u 238 u 230 th the activity ratios observed in the regolith samples are explained by i loss of u series isotopes during water rock interactions and ii re deposition of u series isotopes downslope loss of u and th initiates in the meter thick zone of bedrock that cannot be augered but that nonetheless consists of up to 40 clay silt sand inferred to have lost k mg al and fe apparent equivalent regolith production rates calculated with these isotopes for these profiles decrease exponentially from 45 m myr to 17 m myr with increasing regolith thickness from the ridge top to the valley floor with increasing distance from the ridge top toward the valley apparent equivalent regolith residence times increase from 7 kyr to 40 kyr given that the ssho experienced peri glacial climate 15 kyr ago and has a catchment wide averaged erosion rate of 15 m myr as inferred from cosmogenic 10 be we conclude that the hillslope retains regolith formed before the peri glacial period and is not at geomorphologic steady state both chemical weathering reactions of clay minerals and translocation of fine particles colloids are shown to contribute to mass loss of u and th from the regolith consistent with major element data at ssho this research documents a case study where u series isotopes are used to constrain the time scales of chemical weathering and regolith production rates regolith production rates at the ssho should be useful as a reference value for future work at other weathering localities

weathering patterns in high latitude regolith 1 large areas distributed on the earth s surface are covered by regolith an unconsolidated heterogeneous material overlying bedrock in high latitude areas most of the land surface has been reworked and eroded by both glacial and fluvial processes leaving only remnants of formerly extensive regolith covers in an effort to further the understanding of weathering patterns and processes in old regolith covers a comprehensive study of localities spread across norway was carried out on the basis of the distribution of minerals and elements within regolith as well as its internal structure and geomorphologic setting we ascertained that it was formed in situ and originated in pre quaternary times there are similarities between the study sites with respect to regolith thickness zonation and composition the chemical index of alteration cia and the weathering index of parker wip suggests that the degree of chemical weathering in the regolith is advanced compared to the parental bedrock with a maximum change of over 80 which indicates a substantial increase in the proportion of secondary versus primary minerals mineral analysis identified kaolinite and gibbsite which are considered indicative of advanced weathering and therefore support this observation on the basis of statistical relationships between different grain size fractions 125 m we observed a consistent pattern which revealed that physical weathering becomes progressively less important in the production of grains smaller than 32 m on the basis of this finding we infer that chemical weathering progressively dominates the production of fine silt very fine silt and clay whereas physical weathering primarily controls the production of grain size fractions larger than 32 m this particular pattern is suggested to be an intrinsic feature in the formation of weathered high latitude regolith

predicting radioactive accessory mineral dissolution during chemical weathering the radiation dose at the solubility threshold for epidote group detrital grains from the yangtze river delta china abstract the influence of heavy ion irradiation on the solubility of natural epidote group minerals has been investigated the epidote group are calc silicate minerals that if soluble during terrestrial chemical weathering are capable of consuming atmospheric co 2 over geologic time the experimental design was to calculate the particle dose for actinide rich epidote group grains from the deltas of rivers draining large watersheds large watersheds should yield a suite of epidote group grains spanning the range of compositions and radiation damage commonly observed in nature these grains would be resistant to dissolution during chemical weathering and survive into fluvial sediments therefore the highest particle dose calculated for the suite of grains represents a minimum solubility threshold for the epidote group minerals during chemical weathering the particle dose is calculated from the 232 th 238 u and 235 u content of a grain and the grain s date actinide rich epidote group grains were isolated from yangtze river and river nile delta sediments although only the grains from the yangtze delta had 232 th 208 pb ratios sufficiently high to yield meaningful dates a total of 28 th rich epidote group grains were isolated from the yangtze delta sediment with 24 being classified as allanite and four being classified as ree rich epidote isotopic ratio data were measured by laser ablation microprobe inductively coupled plasma mass spectrometry dates and ree patterns revealed at least 17 different sources of grains with tho 2 contents ranging from 0 057 to 4 37 wt and dates ranging from 32 2 to 3788 263 ma the calculated maximum particle dose of the suite of yangtze delta epidote group mineral grains and hence the minimum solubility threshold is 7 1 10 15 decay mg 1 therefore to predict the likelihood of an epidote group mineral dissolving during chemical weathering at a specific study site the particle dose may be calculated from the date of the rock even if estimated and the radioactinide concentrations of the mineral a calculated particle dose below 7 1 10 15 decay mg 1 likely reflects epidote group mineral stability during chemical weathering calculation of the particle dose may be superior to microscopic identification of accessory the particle dose at the solubility threshold of 7 1 10 15 decay mg 1 value is approximately double that reported for zircon therefore relative to zircon epidote group minerals can withstand more radiation prior to becoming soluble this finding is surprising considering the chemical durability of zircon this substantial variance in solubility threshold radiation doses between the two minerals cannot be explained by the bond strengths of non tetrahedral cations and structural oxygen which are lower in allanite than zircon

resolving the integral connection between pedogenesis and landscape evolution abstract soil is central in the terrestrial ecosystem linking and providing feedback responses to the other components i e water atmosphere and vegetation however the role of soil in landscape evolution is usually not well acknowledged in modeling landscape evolution soil is only treated as a residue of weathering that is transported and redistributed along the hillslope weathering is considered as a process that produces clays and generates unconsolidated materials available for erosion while pedology has been debating the form of qualitative factorial models for 75 years models for soil water heat solute gas and chemical reactions in a profile have matured as soils are distributed continuously in three dimensions across landscapes the profile models need to consider lateral fluxes this review outlines the role of soil in landscape modeling first we review the role of soil in the current landscape evolution models we then review data and models on soil weathering rates and transport processes we discuss soil profile models that simulate soil formation processes and combined soil landscape evolution models finally we discuss how the models can be tested and validated in the real world and suggest how both soil scientists and landscape modelers can work together to address the grand challenges in modeling earth surface processes

a synoptic and statistical description of the gulf stream and subtropical gyre using sofar floats abstract trajectories of 17 sofar floats ballasted to nominal depth of 700 and 2000 m and tracked for 15 months have been analyzed to produce synoptic and statistical descriptions of the gulf stream and subtropical gyre sofar floats launched in and near the gulf stream along with positions of the surface gulf stream and satellite tracked buoys demonstrate strong baroclinic shear nevertheless the horizontal patterns of the gulf stream meanders and gulf stream rings are the same at the surface and at 700 and 2000 m depth above the thermocline particle speeds greater than the propagation speed of the meanders cause parcels of water to move with the flow pattern at greater depths the velocities are at most equal to the propagation speed and the deep trajectories are free to pass through the gulf stream or ring strong temporal variability is found near the tail of the grand banks instances of flow both southward into a narrow gulf stream recirculation and northward into the north atlantic current can

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

multi proxy records of quaternary fluvio lacustrine sediments around lakes eymir and mogan ankara central anatolia turkey this paper presents the mineralogical geochemical palynological and stable isotopic compositions of the late pleistocene holocene fluvio lacustrine sediments around lakes eymir and mogan ankara central anatolia it is based on the interpretation of the multi proxy records in conjunction with the geochronological data in eight different sections the comparison between the increase decrease in the abundances of carbonates and total clay assemblages is correlated with the changing abundance of coniferous forests and herbaceous plants mainly asteraceae and chenopodiaceae 13c and 18o values and molecular weathering ratios of the sediments revealing the hydrolysis evaporation and leaching together with chemical index of alteration cia provide insight into the climatic changes in the study area between 11 899 and 1428 cal year bp relatively higher total clay amount 18o of around 8 and higher cia 40 with higher hydrolysis suggest humid conditions during 11 899 6448 cal year bp between 6448 and 5763 cal year bp sediments show oscillations between high and relatively low values of the proxy data implying intercalation of dry and wet seasons the last period recorded between 5763 and 1428 cal year bp is realized with high calcite precipitation low total clay and low cia and relatively higher salinization which directly characterize aridity

the sources and mixing characteristics of the agulhas current recent observations taken at four principal latitudes in the agulhas current show that the watermass properties on either side of its dynamical core are significantly different inshore of its velocity core are found waters of predominantly arabian sea red sea and equatorial indian ocean origin while offshore waters are generally from the atlantic ocean the southern ocean and the southeast indian ocean for the most part the inshore waters approach the agulhas current through the mozambique channel while those offshore are circulated within the southern indian ocean subtropical gyre before joining the current these disparate water masses remain distinct during their 1000 km journeys along the south african continental slope despite the convergence extreme velocity shears and high eddy kinetic energies found within the agulhas current both potential vorticity conservation and kinematic arguments are discussed as potential inhibitors of along isopycnal mixing it is concluded that a high cross stream gradient of potential vorticity is the dominant mechanism for watermass separation near the surface while the kinematic steering of water particles by the current is dominant at intermediate depths where cross stream potential vorticity is homogeneous hence three lateral mixing regimes for the agulhas current are suggested the surface and thermocline waters are always inhibited from mixing by the presence of both a strong cross frontal potential vorticity gradient and kinematic steering at intermediate depths mixing is inhibited by steering alone and thus in this regime periodic mixing is expected during meander events such as natal pulses when the steering level will rise and allow cross frontal exchange below the steering level in the deep waters there is a regime of free lateral mixing the deep waters of the agulhas current are homogeneous in the cross stream sense being from the same north atlantic source and their salinity steadily and rather rapidly decreases to the north here it is suggested that mixing must be dominated by vertical processes and a large vertical mixing coefficient of order 10 cm 2 s 1 is estimated

how mineralogy and slope aspect affect ree release and fractionation during shale weathering in the susquehanna shale hills critical zone observatory abstract to understand the factors that control rare earth elements ree release and fractionation during shale weathering we investigate the ree contents in solid bedrock regolith stream sediments and natural waters stream and pore waters from a first order catchment developed entirely on gray shales in central pennsylvania usa up to 65 of the ree relative to parent bedrock is depleted from the weathering profiles in the acidic and organic rich soils due to chemical leaching in addition newly formed fine particles were also lost along with the down slope movement of soil waters weathering profiles on the south facing slope show less depletion of ree than those on the north facing slope 33 vs 45 on average we hypothesize that the different degrees of ree depletion on the two transects reflect a history of different chemical weathering rates and possible different surface erosion rates controlled by contrasting slope aspect induced microclimate conditions in addition weathering profiles natural waters and sequential extractions all show a preferential removal of middle ree up to 22 more relative to light ree and heavy ree during shale weathering due to preferential release of mree from rhabdophane furthermore the long term phosphate mineral dissolution rates e g rhabdophane were estimated at 10 15 to 10 14 mol m 2 s 1 under field conditions based on ree depletion profiles strong positive ce anomalies average ce ce n value 1 79 observed in the regolith stream sediments and regolith extractions point to the fractionation and preferential precipitation of ce as compared to other ree due to the generally oxidizing conditions during release transport and redistribution of ree in the surface and subsurface environments positive eu anomalies average eu eu n value 1 30 observed in the natural waters of the catchment are attributed to weathering of plagioclases in the shale bedrock this study highlights the use of ree as natural tracers for low temperature geochemical processes

isotopic evidence for temperature variation during the early cretaceous late ryazanian mid hauterivian oxygen and carbon isotopic compositions have been determined from the belemnite genera acroteuthis and hibolites sampled from the early cretaceous ryazanian hauterivian interval of the speeton clay formation filey bay england the speeton clay formation consists of a series of claystones and calcareous mudrocks deposited in an epicontinental sea 18 o values from belemnites which met petrographic and chemical criteria for well preserved skeletal carbonate indicate warm marine palaeotemperatures c 12 15 c for much of the early valanginian whilst cool temperatures

fast microscale controlled weathering of rhyolitic obsidian to quartz and alunite abstract six year experiments of volcanic glass reacting with waters of different chemistry two freshwaters seawater and brine at 22 c have produced the thorough transformation of mm size glass chips into quartz with minor alunite and calcite these results contradict the current thinking about glass weathering and quartz formation the reaction from glass to quartz took place at an estimated velocity ranging from 300 2000 times to 10 6 times faster than the accepted values for quartz precipitation depending on how rates were assessed the most likely process taking place is the rapid transformation of cation depleted glass into quartz in addition alunite formed very efficiently from low s glass 40 15 ppm such effective reaction in the absence of the accepted conditions for alunite formation is attributed to the high al and k content combined with the generation of low ph conditions at the microscale local low ph conditions may arise due to proton for na substitution at the earliest stage followed by liberation of the protons as glass later corroded the surprising results show a new pathway of glass weathering and point towards reactions controlled by microscale conditions producing high activities locally such conditions may be common in the mineral fluid interface with saline waters immobile waters or systems with low water rock ratios the rapid precipitation of quartz at low temperature is relevant to the origin of quartz and the silica budget in a variety of sedimentary environments and prompts their reconsideration

temperature dependence of silicate weathering in nature how strong a negative feedback on long term accumulation of atmospheric co2 and global greenhouse warming estimation of the temperature dependence of natural feldspar weathering in two catchments at different elevations yields an apparent arrhenius activation energy of 18 4 kcal mol 77 0 kj mol much higher than most laboratory values this finding supports recent suggestions that hydrolytic weathering of silicate minerals may consume carbonic acid and thereby remove atmospheric carbon dioxide more rapidly with increasing temperature than previously thought this result provides a stronger negative feedback on long term greenhouse warming than has been assumed in most models of global carbon cycling the present estimate was determined from the ratio of feldspar weathering rates determined by geochemical mass balance in the southern blue ridge mountains of north carolina united states temperature a function of elevation is the only factor that differs between the two catchments parent rock type aspect hillslope hydrology and vegetation type and successional stage are the same in both

rare earth element trends and cerium uranium manganese associations in weathered rock from koongarra northern territory australia at koongarra australia three drill cores form the cahill schist formation containing u ore and regolith above it containing secondary u ore were studied to ascertain the distribution of rare earth elements rees and u the unaltered schist has a ree trend similar to the post archaean australian shale paas which is therefore used as a normalising standard unweathered rock from the zone of primary u mineralisation contained strong enrichment of the heavy rees and this pattern is retained during most of the weathering strongly bleached and very weathered shallow samples from this zone do not show enrichment of hrees in general however weathering appears to have little effect on the pattern of rees in the bulk rock at this site zones rich in mn oxy hydroxides occurring as coatings on fissure surfaces contain large concentrations of ce and u with a clear ce anomaly ce ce 3 8 the ce and u apparently occur together as microcrystalline oxides within 1 2 mu m diameter globules on mineral surfaces in the mn rich zones 46 refs 10 figs 2 tabs

inverse models to analyze the spatiotemporal variations of chemical weathering fluxes in a granito gneissic watershed mule hole south india water rock reactions are driven by the influx of water which are out of equilibrium with the mineral assemblage in the rock here a mass balance approach is adopted to quantify these reactions based on field experiments carried out in a granito gneissic small experimental watershed sew mule hole sew similar to 4 5 km 2 quartz oligoclase sericite epidote and chlorite are identified as the basic primary minerals while kaolinite goethite and smectite are identified as the secondary minerals observed groundwater chemistry is used to determine the weathering rates in terms of mass transfer coefficients mtcs of both primary and secondary minerals weathering rates for primary and secondary minerals are quantified in two steps in the first step top red soil is analyzed considering precipitation chemistry as initial phase and water chemistry of seepage flow as final phase in the second step minerals present in the saprolite layer are analyzed considering groundwater chemistry as the output phase weathering rates thus obtained are converted into weathering fluxes q weathering using the recharge quantity spatial variability in the mineralogy observed among the thirteen wells of mule hole sew is observed to be reflected in the mtc results and thus in the weathering fluxes weathering rates of the minerals in this silicate system varied from few 10 mu mol l in case of biotite to 1000 s of micromoles per liter calcite similarly fluxes of biotite are observed to be least 7 5 mol ha yr while those of calcite are highest 1265 791 mol ha yr further the fluxes determined annually for all the minerals are observed to be within the bandwidth of the standard deviation of these fluxes variations in these annual fluxes are indicating the variations in the precipitation hence the standard deviation indicated the temporal variations in the fluxes which might be due to the variations in the annual rainfall thus the methodology adopted defines an inverse way of determining weathering fluxes which mainly contribute to the groundwater concentration c 2011 elsevier b v all rights reserved

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