behavior of rare earth elements in a paleoweathering profile on granodiorite in the front range colorado usa abstract a paleoweathering profile on the boulder granodiorite in northern colorado provides an opportunity to trace the behavior of rees from parent rock through a weathering profile into unconformably overlying permian sediments with progressive upward weathering of the granodiorite na2o cao sio2 ta hf co th cr sc cr th zr hf la sc zr y and la th decrease al2o3 and fe2o3t increase and tio2 mgo k2o p2o5 rb zr sc cr co hf nb ta y th u ree ti nb and zr nb increase to maximum values and then either level off or decrease lree enrichment is less in the weathering profile than in the parent granodiorite and although the parent does not have an eu anomaly or only a slight positive anomaly all samples from the weathering profile and overlying sediments have significant negative eu anomalies this observation is especially important in that it shows conclusively that a negative eu anomaly can be produced during chemical weathering of granitoids we suggest these eu anomalies are due to relative enrichment of the other rees and partial loss of eu during the breakdown of plagioclase the boulder weathering profile also has a very minor negative ce anomaly that is within error of a ce anomaly in the parent in the unweathered parent 50 of the ree are contained in sphene and in the case of la also in allanite from 10 20 of the ree are contained in apatite and biotite hornblende and from 7 10 of the hrees are in zircon with exception of eu for which feldspars contribute about 8 negligible amounts of rees occur in the feldspars in weathered samples 75 of the rees are contained in clay minerals the crossover between sphene and clay control of rees occurs over a distance of 1 m near the contact with fresh rock except for their small negative eu anomalies the clay minerals have ree patterns very similar to those of the parent rock isocon plots suggest apparent enrichments of many elements in the boulder weathering profile result from losses of na ca and si during plagioclase weathering in addition variable amounts of sr eu ta nb p and ba were lost during weathering although th u zr y th sc zr hf lu hf and ti zr may have been transferred relatively unchanged from granodiorite parent to the bulk weathering profile most other element ratios and ree distributions were significantly changed during weathering this observation implies that caution needs to be exercised when using ree patterns and element ratios to trace sediment provenance the fact that most element ratios and ree distributions also differ between fountain sediments and the bulk weathering profile may be related to one or a combination of four factors listed in order of probable decreasing importance contribution of other sources to the fountain sediments sorting of minerals during sediment deposition remobilization of elements during diagenesis and leaching of elements by water flow through the upper meter of the weathering profile

mobility and fractionation of rees during deep weathering of geochemically contrasting granites in a tropical setting malaysia in this study we describe the mobility and fractionation of rees in two deep up to 30 m tropical weathering profiles developed on two granites from the kuala lumpur pluton malaysia sampled at cheras and rawang on the basis of na2o and k2o both are s type granites but rawang has higher cao mgo and feo than cheras and lower sio2 with respect to al saturation rawang is i type and cheras is s type we compared the two profiles in terms of total rees magnitude and changes in ce and eu anomalies ree mobility and lree hree fractionation rawang profiles have higher ree contents display lower mobility for most except the heaviest rees and show higher lree hree fractionation than those from cheras these differences can be linked to differences in primary mineralogy and degree of weathering the latter controlling the type and volume of secondary minerals specifically bowl shaped parent rock normalised patterns in the cheras saprolites appear to be a result of apatite dissolution moreover moderate weathering evident in lower mineralogical indices of alteration mia at cheras has conserved parent rock ree patterns and fractionation factors in the saprolites by contrast more intense weathering observed in rawang profiles has produced abundant kaolinite group minerals that have preferentially retained lree which consequently display high lree hree fractionation this study provides important insights into the factors controlling ree mobility during tropical weathering and its potential as an indicator of weathering intensity

early cretaceous terrestrial weathering in northern china relationship between paleoclimate change and the phased evolution of the jehol biota abstractthe jehol biota from lower cretaceous deposits in northern china provides an important record of terrestrial fauna and flora including feathered dinosaurs and one of the earliest angiosperms this biota underwent three development phases with a relatively limited biodiversity in the early phase that rapidly diversified in the middle phase this study analyzes the conditions of terrestrial paleoweathering during the lower cretaceous as inferred from the geochemistry of mudstones with the aim of assessing the role of paleoclimate change as a background factor that led to the phased evolution of the jehol biota the analysis focuses on the dabeigou and dadianzi formations of hebei province northern china which record the early and middle phases of the jehol biota respectively these fluviolacustrine sequences can be lithologically divided into lower and upper units geochemical weathering indices e g w ree total amount of rare earth elements and w show a significant increase from the

minero petrographical features of weathering profiles in calabria southern italy abstract the paper reports interdisciplinary research of weathering profile stages on gneiss with regard to tectonic and landscape evolutions of the western sila grande massif southern italy the outcropping rocks consist of medium to coarse grained biotite garnet and sillimanite gneiss bgs g and medium to coarse grained biotite muscovite migmatitic gneiss m g the bgs g rocks are fractured and weathered with either massive or foliated texture whereas the m g rocks are intensely weathered and fractured with a massive texture and frequent pegmatite veins petrographical and mineralogical variations show that both gneissic rocks bgs g and m g samples underwent weathering processes characterized by a progressive chemical attack on the labile minerals with generation of neoformed minerals and substitution of the original rock fabric the weathering processes produced phyllosilicates and fe oxides neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage microfractures and morphological variations occur on the original rock and thereby affect the surrounding landscape processes the weathering profile mineralogy and rock textures viewed in the context of landscape evolution provide useful insights into the widespread slope movement phenomena in the sila grande massif gneiss

the source and origin of terrigenous sedimentary rocks in the mesoproterozoic ui group southeastern russia abstract arenites wackes and associated shales and siltstones of the ui group of riphcan age in southeastern siberia have been analyzed for petrographic major element and selected trace element compositions including the ree petrographic results suggest that the arenites may have been derived from granites and that the wackes may have been derived from more plagioclase rich rocks like tonalites or granodiorites the high quartz relative to other materials in many sandstones suggest that they may have been derived from intense chemical weathering or diagenesis so the mineralogic ratios may have been changed during these processes the shales and siltstones are composed mostly of illite and quartz in addition a cn k diagrams indicate that the wackes and associated shales and siltstones underwent k metasomatisim extrapolation of the shales and siltstones associated with the wackes back to the plagioclase alkali feldspar line in the a cn k diagram suggests a high average plagioclase to alkali feldspar ratio in the provenance tonalite to granodiorite extrapolation of shales and siltstones associated with the arenites suggest a low plagioclase to alkali feldspar ratio in the provenance granite in addition the index of compositional variability icv and chemical index of alteration cia parameters of the shales and siltstones suggest the weathering of the first cycle material was intense trace element ratios suggest all the sedimentary rocks were derived from mostly granitoids shales and siltstones were plotted as elemental ratios e g th sc vs eu eu these plots suggest a mix of a granodiorite tonalite source for the source of the shales and siltstones associated with the wackes with a granite source for the shales and siltstones associated with the arenites the arenites also contain lower eu eu and higher th co and th sc ratios than the wackes this as is consistent with the petrography suggests that the arenites were derived from a source with more granite and less granodiorite tonalite than the wackes

chemical overprinting of magmatism by weathering a practical method for evaluating the degree of chemical weathering of granitoids abstract quantitative determination of the degree of chemical weathering of rocks is a fundamental task in environmental and engineering geology and many weathering indices based on whole rock chemistry have been proposed however most classical indices are of limited application to granitoids in a wide area because these lithotypes generally exhibit wide chemical variation arising from their petrogenesis the chemical evolution produced during rock weathering therefore overprints pre existing magmatic chemical variation this problem can cause many classical weathering indices to yield misleading results this study proposes a method that compensates for the influence of petrogenesis on calculation of the weathering index the method is based on a bivariate plot of the magmatic chemical variation mcv in granitoids and the degree of chemical weathering dcw the mcv axis must be based on an element that reflects magmatic processes and is also relatively immobile during rock weathering in this study tio 2 contents are utilized for the mcv the dcw axis is fundamentally defined by the ratios of more mobile to less mobile elements during weathering and hence many classical indices can be applied the improved value of the degree of chemical weathering dcw i for a weathered rock is derived by dcw i s mcv cv mcv 1 dcw 1 where mcv 1 is the measured composition e g tio 2 content of the weathered rock dcw 1 denotes the ratios of more mobile to less mobile elements of the weathered rock the s parameter is the slope of the least square linear regression for fresh granitoids in the mcv dcw relationship mcv cv is a correction factor which is given by the average point on the mcv axis e g average tio 2 of the fresh rocks this method is useful for evaluating the degree of weathering of various granitoids and enhances the practical application of many weathering indices

chemical weathering of crystalline rocks in contrasting climatic conditions using geochemical proxies an overview abstract weathering profiles of granitoid rocks from the sila massif southern italy have been studied to characterize weathering processes that affect this area chemical weathering indices of the sila massif weathered granitoids were compared to those of different areas of the world characterized by different climates malaysia puerto rico georgia china nigeria colorado switzerland and sweden to decipher their weathering characteristics the geochemical indices show values of cia chemical index of alteration ranging from 55 to 97 ciw chemical index of weathering ranging from 60 to 100 pia plagioclase index of alteration ranging from 55 to 100 wip weathering index of parker ranging from 7 to 64 and rr ruxton ratio ranging from 2 14 to 3 96 all these geochemical proxies closely resemble each other and show variations mainly related to the different climatic and tectonic settings malaysia and puerto rico granitoids showing high cia values respectively 97 and 95 on average underwent very intensive chemical weathering alteration georgia china and nigeria showing medium high cia values respectively 86 90 and 92 on average underwent moderate intensive chemical weathering alteration southern italy and colorado granitoids showing medium low cia values 68 on average underwent moderate weak chemical weathering alteration whereas switzerland and sweden granitoids showing low cia values respectively 58 and 55 on average underwent weak chemical weathering alteration those values are mainly related to the climatic conditions in term of temperature and precipitation of each area cia vs climate histograms display a shift towards higher cia values with increasing of warm humidity tropical conditions whereas granitoids weathered under conditions inferred to be cold arid polar climate show lower cia values

silicate weathering of soil mantled slopes in an active alpine landscape abstract despite being located on high steep actively uplifting and formerly glaciated slopes of the swiss central alps soils in the upper rhone valley are depleted by up to 50 in cations relative to their parent bedrock this depletion was determined by a mass loss balance based on zr as a refractory element both holocene weathering rates and physical erosion rates of these slopes are unexpectedly low as measured by cosmogenic 10be derived denudation rates chemical depletion fractions cdf range from 0 12 to 0 48 while the average soil chemical weathering rate is 33 15 t km 2 yr 1 both the cosmogenic nuclide derived denudation rates and model calculations suggest that these soils have reached a weathering steady state since deglaciation 15 ky ago the weathering signal varies with elevation and hillslope morphology in addition the chemical weathering rates decrease with elevation indicating that temperature may be a dominant controlling factor on weathering in these high alpine basins model calculations suggest that chemical weathering rates are limited by reaction kinetics and not the supply rate of fresh material we compare hillslope and catchment wide weathering fluxes with modern stream cation flux and show that high relief bare rock slopes exhibit much lower chemical weathering rates despite higher physical erosion rates the low weathering fluxes from rocky rapidly eroding slopes allow for the broader implication that mountain building while elevating overall denudation rates may not cause increased chemical weathering rates on hillslopes in order for this sediment to be weathered intermediate storage for instance in floodplains is required

absolute and relative plate motions and hypotheses on the origin of five aseismic ridges in the indian ocean abstract paleopositions of the african indian and antarctic plates are used as an independant set of data to test various hypotheses derived from geophysical data on the origin emplacement mechanism and evolution of five aseismic structures of the western and southern indian ocean crozet and kerguelen plateaus marion dufresne lena and ob seamount chain madagascar and mascarene ridges except for a continental fragment of very limited extent bearing the seychelles islands these structures together with the madagascar and mascarene ridges are probably due to anomalous volcanic episodes at or near active plate boundaries rather than to intraplate emplacement their creation processes are therefore mainly related to the relative motions between the antarctic african and indian plates the volcanic episodes are synchronous with major changes in the relative motions between these plates and thus substantiate the role played by frequent irregularities in the kinematic pattern of the western and southern indian ocean such as ridge jumps asymmetric spreading and rapid variations in spreading velocity or direction finally we think that thermal anomalies located not far from active spreading boundaries may have played a role in the physical processes creating the aseismic ridges

quaternary bedrock erosion and landscape evolution in the sor rondane mountains east antarctica reevaluating rates and processes abstract rates and processes of rock weathering soil formation and mountain erosion during the quaternary were evaluated in an inland antarctic cold desert the fieldwork involved investigations of weathering features and soil profiles for different stages after deglaciation laboratory analyses addressed chemistry of rock coatings and soils as well as 10be and 26al exposure ages of the bedrock less resistant gneiss bedrock exposed over 1 ma shows stone pavements underlain by in situ produced silty soils thinner than 40 cm and rich in sulfates which reflect the active layer thickness the absence of cryoturbation and the predominance of salt weathering during the same exposure period more resistant granite bedrock has undergone long lasting cavernous weathering that produces rootless mushroom like boulders with a strongly fe oxidized coating the red coating protects the upper surface from weathering while very slow microcracking progresses by the growth of sulfates geomorphological evidence and cosmogenic exposure ages combine to provide contrasting average erosion rates no erosion during the quaternary is suggested by a striated roche moutonnee exposed more than 2 ma ago differential erosion between granite and gneiss suggests a significant lowering rate of desert pavements in excess of 10 m ma 1 the landscape has been on the whole stable but the erosion rate varies spatially according to microclimate geology and surface composition

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

understanding antarctic peninsula precipitation distribution and variability using a numerical weather prediction model daily precipitation fields and annual means from the european centre for medium range weather forecasts re analysis exercise are used to examine the distribution and variability of precipitation across the antarctic peninsula the annual mean precipitation field from the model agrees well with the available ice core data and suggests that the maximum accumulation for the area is on the western side of the barrier at about the 200 m level where the annual total is close to 1 3 m w e the peninsula is shown to be a very effective barrier to the zonal movement of precipitati ng weather systems which results in quite different atmospheric flow regimes being responsible or significant precipitation events on either side of the divide frontal depressions are the primary source of large daily snowfall totals on both sides of the peninsula on the southern coast of the bellingshausen sea major snowfall events are often linked to strong northerly flow when the atmospheric circulation is blocked predominantly northerly flow is also responsible for significant snowfall on the ronne ice shelf which often occurs in association with lee cyclogenesis events to the east of the peninsula

sedimentary evolution of the mesozoic continental redbeds using geochemical and mineralogical tools the case of upper triassic to lowermost jurassic monte di gioiosa mudrocks sicily southern italy the continental redbeds from the internal domains of the central western mediterranean chains have an important role in the palaeogeographic and palaeotectonic reconstructions of the alpine circum mediterranean orogen evolution since these redbeds mark the triassic jurassic rift valley stage of tethyan rifting the composition and the sedimentary evolution of the middle triassic to lowermost jurassic continental redbeds of the san marco d alunzio unit peloritani mountains southern italy based on mineralogical and chemical analyses suggests that the studied mudrock sediments share common features with continental redbeds that constitute the internal domains of the alpine mediterranean chains phyllosilicates are the main components in the mudrocks the 10 a minerals illite and micas the i s mixed layers and kaolinite are the most abundant phyllosilicates the amount of illitic layers in i s mixed layers coupled with the illite crystallinity values ic are typical of high degree of diagenesis corresponding to a lithostatic tectonic loading of about 4 5 km the mineralogical assemblage coupled with the a cn k plot suggest post depositional k enrichments palaeoweathering proxies pia and ciw record intense weathering at the source area further the studied sediments are affected by reworking and recycling processes and as consequence it is likely these proxies monitor cumulative effect of weathering the climate in the early jurassic favoured recycling and weathering occurred under hot episodically humid climate with a prolonged dry season the source area is the low grade paleozoic metasedimentary basement mafic supply is minor but not negligible as suggested by provenance proxies

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

global continental weathering trends across the early permian glacial to postglacial transition correlating high and low paleolatitude sedimentary records time equivalent early permian sedimentary successions from high latitude gondwana basins and from equatorial accumulations in north china covering the glacial to postglacial transition display correlatable trends in continental weathering intensity based on chemical index of alteration cia values the successions display a pattern of cia values that varies with latitude similar to modern estuarine suspended sediments based on the modern day cia temperature correlation the glacial early permian low to high latitude land surface temperature gradient is estimated as 20 c slightly higher than the calculated values for the contemporaneous sea surface temperature gradient

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

volcanic soil formation in calabria southern italy the cecita lake geosol in the late quaternary geomorphological evolution of the sila uplands abstract this paper focuses on the main morphological physical chemical and mineralogical features of an andic like soil widely outcropping in the sila upland plateau of calabria southern italy and its potential role in tephrostratigraphy a multidisciplinary and multiscale approach allowed identification of this soil as a masked distal archive of volcanic products developed on granite rocks and sediments with a coeval pyroclastic input during pedogenesis the study demonstrates that the contribution of volcanic parent materials can be successfully hypothesized and assessed even in the absence limited extent or poor preservation of primary eruptive products the soil has an andisol like appearance despite laboratory data that do not match the entire suite of diagnostic criteria for the andisol taxonomic order geomorphological stratigraphic and pedologic results coupled with tephrostratigraphic and radiometric data concur to suggest a late pleistocene to holocene age of the andisol like soil in particular the rhyolitic chemical composition of small sized glass fragments identified by sem eds analyses indicates soil genesis contributed by volcanic ash probably sourced from aeolian arc explosive activity spanning the last 30 ka accordingly the evidence of limited relict clay illuviation and the specific type of pedogenesis allowing the development of andic properties in turn related to the neoformation of clay minerals from the weathering of volcanic glass are consistent with a climatic shift from a seasonally contrasted to a constantly humid pedoenvironment this change can be ascribed to the lateglacial or early middle holocene to late holocene transition calibrated ams 14 c dates performed on charcoal fragments sampled from three representative soil profiles provide late holocene ages 3136 19 343 16 and 92 24 yr bp in accord with archaeological finds on the basis of the consistent stratigraphic position lateral continuity and wide extent the soil can be considered a good pedostratigraphic marker in the sila highlands and is informally defined as the cecita lake geosol it supplies valuable time constraints for the underlying occasionally overlying deposits and or soils moreover it allows regional scale morphostratigraphic correlations and detailed reconstruction of late pleistocene holocene geomorphic events in calabria a very suitable region for distal tephra deposition in the central mediterranean peri volcanic area the effects of high energy volcanic eruptions are interfingered with or superimposed by other geomorphic processes and climatic or anthropogenic signals

holocene tectono geomorphic evolution of parts of the upper and middle gangetic plains india abstract using multispectral scanning mss images and digital elevation models dems 26 terrain morphological units were delineated in the study area between the rapti and kosi rivers in the gangetic plains based on the degree of soil development and the infrared stimulated luminescence chronology these terrain morphological units have been grouped into six members of a morphostratigraphic sequence with ages 1 65 1 65 5 3 5 3 7 5 7 5 8 5 8 5 10 and 10 ka integrated use of geomorphic markers including different drainage patterns identified from mss images significant breaks in topographic profiles terminal fans and artifact terrain features e g cliffs and significant breaks in slopes in dems digital terrain models dtms with highly exaggerated vertical dimensions were made to infer and map 20 nascent faults in the region between the ghaghara and kosi rivers in the flat gangetic plains the three major tectonic blocks are the upland ghaghara rapti block of the upper gangetic plain and the rapti gandak and gandak kosi blocks of the middle gangetic plain marked by high rates of subsidence and sedimentation the ghaghara rapti block bounded by the incised ghaghara and rapti rivers is an upland region and is primarily overlain by 10 ka old soils subsequent activity along the ne sw trending transverse normal faults led to deposition of young terminal fans southward tilt of the ghaghara rapti block generated two e w trending terraces on the left bank of the ghaghara river southwestward tilting of the upper part of the ghaghara rapti block led to development of the widest old ghaghara plain and rapti floodplain in the sw direction northeastward tilting of the rapti gandak block shifted the gandak river from west to east over a distance of 80 km during the period from 10 to 8 5 ka further compression from the sw caused development of four extensional normal faults the activity of three faults between 5 7 and 1 0 ka generated four terminal alluvial fans on this block the gandak kosi block is marked by a set of seven thrust splays off the himalayan frontal thrust hft in the footwall activity of these thrust splays in the foothill region caused progradation of the gravel piedmont and thus developed the widest piedmont zone 124 km in the gangetic plains this is the first report of gravel piedmont progradation from a modern environment and role of thrust splays in such a progradation in the southernmost part of this block the continuous occurrence of terminal fans over a length of 140 km south of the south muzaffarpur fault forms a terminal fan piedmont bajada orientation of the faults was used to interpret compression from the sw in the ghaghara rapti interfluve plain in the west since 10 ka and compression from the south in the gandak kosi interfan region in the east after 4 5 ka the rapti gandak region in the central part shows the effects of mainly compression from the sw and compression from the south at different times in addition to terminal fans formed because of low relief terrain features created by the activity of faults by involvement of the entire discharge of small meandering braided streams a new type of fan formed by splays from a large river on the downthrown sides of faults called splay terminal fans is observed from the rapti gandak block

the influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern united states this paper reports systematic changes in mudrock composition through time on a single con tinental cmstal block the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton the major and trace element distributions reflect different aspects of the provenance of the mudrocks in this study major elements record sediment recycling processes as well as changing proportions of sedi mentary and first cycle source rocks with the exceptions of kzo which tends to increase and sioz and a o3 which show no trend most major oxides tend to decline in relative abundance in younger mud rocks patterns shown by the index of compositional variability fe03 kro naao cao mgo mno tiojialro and by k20 a1203 indicate that the major oxide trends are due to decreasing proportions of nonclay silicate minerals and a concomitant increase in the proportion of clay minerals probably due to decreasing input of first cycle detritus coupled with recycling of sedimentary material excursions from progressive trends marked by increases in mgo k20 and cao reflect episodes of large scale input of nonclay first cycle minerals from crystalline source rocks due to large scale basement uplift the chemistry of low solubility trace elements in contrast is not sensitive to recycling effects and reflects the composition of first cycle input incompatible elements are progressively enriched relative to compatible elements in younger mudrocks and values for chondrite normalised rare earth elements also increase in addition the eu anomaly becomes systematically more negative in younger samples these trends cmnot be explained by diagenetic or weathering processes and therefore indicate that the proportion of fnc tionated granitic first cycle detritus being added to the sedimentary system becomes greater with time these results confirm the importance of tectonic setting in controlling mudrock chemistry and also demonstrate that there is a dynamic relationship between the tectonic evolution of a continental block and the composition of its sedimentary mantle

weak influences of climate and mineral supply rates on chemical erosion rates measurements along two altitudinal transects in the idaho batholith 1 chemical weathering promotes regolith production physical erosion nutrient supply and drawdown of atmospheric co2 although mineral dissolution rates show dependences on temperature and moisture in theoretical models and laboratory experiments effects of climate on chemical erosion rates in nature remain uncertain in part because variations in physical erosion rates and lithology can obscure climatic signals in chemical erosion rate measurements here we present new estimates of millennial scale chemical and physical erosion rates along two altitudinal transects in the idaho batholith our measurements suggest that chemical erosion rates and the extent of regolith chemical alteration are insensitive to mean annual regolith temperature even though the study sites span a wide range in temperatures 4 8 c 10 9 c these data also suggest that rates of chemical erosion and the extent of regolith chemical alteration are weakly correlated with the annual duration of high regolith moisture conditions lastly our measurements show that the sampled regoliths tend to grow more chemically weathered with increasing regolith residence time implying that weathering at these sites is primarily limited by mineral dissolution kinetics rather than mineral supply rates to the regolith the lack of strong control by mineral supply means that chemical erosion rates at these sites could potentially vary in response to climatic factors such climatically driven variation in chemical erosion rates is not obvious in our data however instead our measurements suggest that chemical erosion rates at these sites are insensitive to mean annual regolith temperature and only weakly dependent on the length of the wet season

10be analysis of a quaternary weathering profile in the virginia piedmont samples from a residual weathering profile in the virginia piedmont have been analyzed for cosmogenic 10be concentrations are highest in clay rich soil and decrease exponentially to a depth of about 15 m despite uncertainties about the processes by which 10be may be intercepted before entering the solum and eroded after incorporation a minimum age may be calculated for the regolith this calculation is based on the delivery rate of 10be and its decay rate and suggests that this residual profile developed during a period no shorter than 8 105 yr the calculated minimum age may be within a factor of 2 of maximum age estimates based on surface lowering by erosion and on the rate of rock weathering to saprolite the vertical distribution of 10be in the profile could result from a steady state balance of deposition weathering radioactive decay and erosion

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

the contribution of nutrients from parent material in three deeply weathered soils of peninsular malaysia three deeply weathered soil profiles developed over basalt granite and schist were studied the isovolumetric calculation was carried out to determine the intensity of elements depleted during weathering the rain and stream waters near the respective areas were sampled and analysed despite the differences in their parent materials the physico chemical properties of the soil proper were quite similar the study generally indicated that the humid tropical rain forests developed over old deeply weathered soils of peninsular malaysia have a closed nutrient cycling system because the contribution of nutrients from the weathering parent material is negligible closed nutrient cycles are favoured by intense weathering at great depth and by the almost complete loss of bases during the rock saprock saprolite transformation the chemical properties of the saprolites are found to be comparable to or even poorer than those of the subsoils so that roots do not have access to the base cations released on initial weathering

global aridity during the early miocene a terrestrial paleoclimate record from the ebro basin spain abstract paleosols are an important tool in the paleoclimatic and paleoenvironmental interpretation of continental deposits and can provide a high resolution proxy for paleoclimate results from geochemical climofunctions applied to early miocene strata exposed in the ebro basin spain demonstrate that mean annual precipitation was the dominant control on paleosol type and indicate that the paleoclimate was considerably wetter during the early miocene by up to 1150 mm yr 1 in comparison to modern values placing it in a subhumid climatic regime rather than an arid semiarid regime as previously suggested by sedimentological and paleontological approaches by making comparisons with published data on paleoclimate during the early miocene this article stresses the importance of regional climatic changes in global paleoclimatic interpretation

paleoclimatic conditions and paleoweathering processes on mesozoic continental redbeds from western central mediterranean alpine chains abstract chemical and mineralogical analyses of the triassic to lowermost jurassic mudstones from continental redbeds outcropping in the internal domains of the betic rifian and calabria peloritani chains have been used to infer the relationships between paleoclimatic conditions and paleoweathering processes during rifting of a continental crust block that finally detached from adjoining western tethyan realms to form an independent microplate mesomediterranean microplate from jurassic to lower miocene time the studied mudstone samples come from middle triassic and upper triassic beds of the saladilla formation both in the betic cordillera and in the rif whereas the calabria peloritani arc studied mudstones come from upper triassic to lowermost jurassic beds both in the sila and longi taormina units major and trace element concentrations based on the mass balance calculation relative to the upper continental crust show negative values both in gibraltar and calabria peloritani arcs implying that mudstone formation in the early mesozoic involved moderate to intense continental paleoweathering of the crust in particular cao na 2 o mgo sr ba fe 2 o 3 mno and transition metal elements v cr co and ni are more depleted in the triassic to upper jurassic samples of the calabria peloritani samples than in the middle to upper triassic betic rifian samples and suggest an increase of continental paleoweathering in the mediterranean region from the triassic to the jurassic in addition enrichment in sio 2 tio 2 al 2 o 3 k 2 o and incompatible elements in the calabria peloritani arc mudstones indicates sediment recycling effects that gradually increase from the triassic to jurassic time the hinterland paleoweathering and sediment recycling effects have been mathematically distinguished using principal component analysis pc1 is a measure of paleoweathering rate mainly due to humidity positive values against aridity negative values whereas pc2 corresponds to the extent of sediment recycling the results strongly indicate that humidity had increased from the triassic to the jurassic and that the depositional environments in calabria peloritani arc were probably more suitable for sediment recycling these seasonal climate alternations corresponding to an increase in paleoclimatic humidity that favored paleoweathering conditions and recycling processes these results are also confirmed by the mineralogical data which show a higher abundance of kaolinite typical of warm humid conditions in the calabria peloritani mudstones than in those of the betic cordillera and the rif furthermore the comparison among geochemical weathering index values of the studied samples and of recent soils from different climatic zones likely suggests a tropical rainforest climate in the studied area during the triassic to the lowermost jurassic

paleoclimatology and provenance of the glaciogenic gowganda formation paleoproterozoic ontario canada a chemostratigraphic approach the gowganda formation dated as about 2 3 ga is widely but not universally interpreted as glaciogenic and our chemostratigraphic study supports such an interpretation the bulk compositions of diamictite matrix materials and associated argillites are considered to have resulted from the mixture of two detrital components one is glacial flour similar in composition to the unweathered archean upper crust whereas the other is chemically weathered detritus resembling average proterozoic shale in composition the first component has a chemical index of alteration cia value of 50 reflecting the abundance of feldspar and dearth of aluminous clay minerals the second component has a cia value of 70 and was produced primarily in weathering profiles by chemical weathering typical of temperate climatic regimes diamictite matrix materials 92 samples have an average cia value of 57 the argillites have higher values the average is 62 97 samples the lower cia values of the diamictites reflect a higher proportion of glacial flour suggesting a stronger influence of frigid climatic conditions than that which prevailed during deposition of the argillites systematic trends in cia values are developed across diamictite argillite boundaries and within a thick argillite between two major diamictite units these values reflect climatic variations with maximum amelioration during deposition of the middle section of the argillite rare earth element data and th sc and ti al ratios from the diamictite matrix materials all suggest a provenance that included a large supracrustal component 45 together with lesser amounts of tonalite trondhjemite granite and granite the proportion of supracrustal materials such as volcanic rocks and shales may have been exaggerated by selective comminution during glacial transport the matrix materials of the gowganda diamictites are severely depleted in ca and proportionally enriched in na relative to the source the anorthitic component of plagioclase has been selectively replaced by an albitic component during diagenesis and metamorphism a chemostratigraphic approach provides high resolution data for reconstruction of paleoclimatic conditions and valuable information concerning provenance and metasomatic processes

clay mineral formation and transformation in rocks and soils three mechanisms for clay mineral formation inheritance neoformation and transformation operating in three geological environments weathering sedimentary and diagenetic hydrothermal yield nine possibilities for the origin of clay minerals in nature several of these possibilities are discussed in terms of the rock cycle the mineralogy of clays neoformed in the weathering environment is a function of solution chemistry with the most dilute solutions favouring formation of the least soluble clays after erosion and transportation these clays may be deposited on the ocean floor in a lateral sequence that depends on floccule size clays undergo little reaction in the ocean except for ion exchange and the neoformation of smectite therefore most clays found on the ocean floor are inherited from adjacent continents upon burial and heating however dioctahedral smectite reacts in the diagenetic environment to yield mixed layer illite smectite and finally illite with uplift and weathering the cycle begins again

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

cosmogenic nuclide based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the swiss alps abstract transient landscape disequilibrium is a common response to climatic fluctuations between glacial and interglacial conditions such landscapes are best suited to the investigation of catchment wide response to changes in incision the geomorphology of the trub and grosse fontanne adjacent stream systems in the napf region of the swiss molasse was analyzed using a 2 m lidar dem the two catchments were impacted by the last glacial maximum lgm even though the glaciers never overrode this region they did however cause base levels to drop by as much as 80 m despite their similar tectonic lithologic and climatic settings these two basins show very different responses to the changing boundary conditions stream profiles in the trub tend to be smooth while in the fontanne numerous knickzones are visible similarly cut and fill terraces are abundant in the trub watershed but absent in the fontanne where deep valleys have been incised the trub appears to be a coupled hillslope channel system because the morphometrics throughout the basin are uniform the morphology of hillslopes upstream of the knickzones in the fontanne is identical to that of the trub basin but different downstream of the knickzones suggesting that the lower reaches of the fontanne have been decoupled from the hillslopes however the rapid incision of the fontanne is having little effect on the adjacent upper hillslopes we tested this interpretation using cosmogenic 10 be derived basin averaged denudation rates and terrace dating the coupled nature of the trub basin is supported by the similarity of denudation rates 350 50 mm ky 1 at a variety of spatial scales upstream of the knickzones rates in the fontanne 380 50 mm ky 1 match those of the trub downstream of the knickzones denudation rates increase to 540 100 mm ky 1 the elevated rates in the downstream areas of the fontanne are due to rapid incision causing a decoupling of the hillslope from the channel basin response time and the magnitude of base level drop exert the principal control over the difference in geomorphic response between the two basins the timing of the filling of the trub valley 17 2 ka and the initial incision of the fontanne 16 3 ka were calculated verifying that these are responses to late glacial perturbations unique lithologic controls allow for one of the fastest regolith production rates yet to be reported 380 mm ky 1

a relict landscape in the centre of fennoscandian glaciation cosmogenic radionuclide evidence of tors preserved through multiple glacial cycles the presence of well developed tors boulder fields and weathering mantles in the parkajoki area of northeastern sweden near the centre of fennoscandian glaciation has been used to suggest that these landscapes were preserved during all glacial cycles since ice sheet initiation in the late cainozoic this implies that all successive large scale glaciations must have had frozen bed conditions across this area to allow for subglacial landscape preservation cosmogenic 10be and 26al data from three tors and a meltwater channel in the parkajoki area were used to test this hypothesis of landscape preservation through multiple glacial cycles apparent exposure ages of tor summit bedrock surfaces ranging between 79 and 37 ka in an area deglaciated at 11 ka are consistent with the interpretation of these features as relict landforms that have survived glaciation with little or no erosion single nuclide minimum exposure age data require that the tors have survived at least two complete glacial cycles this estimate is based on i the approximate duration of periods of ice sheet cover versus ice free conditions as deduced from the dsdp 607 marine benthic foraminifer oxygen isotope record in conjunction with ii a record of fennoscandian ice sheet flow traces and hence ice sheet extent and iii noting that cosmogenic nuclides are accumulated only during ice free periods in addition mean cosmogenic 26al 10be concentration ratios from two of the sites indicate a minimum model total history of 605 ka and a maximum erosion rate of 1 6 m ma 1 thus the numerical ages confirm the overall qualitative interpretation of landscape preservation through multiple glacial cycles

uplift history of the sila massif southern italy deciphered from cosmogenic 10be erosion rates and river longitudinal profile analysis 1 the sila massif in the calabrian arc southern italy is a key site to study the response of a landscape to rock uplift here an uplift rate of 1 mm yr has imparted a deep imprint on the sila landscape recorded by a high standing low relief surface on top of the massif deeply incised fluvial valleys along its flanks and flights of marine terraces in the coastal belt in this framework we combined river longitudinal profile analysis with hillslope erosion rates calculated by 10be content in modern fluvial sediments to reconstruct the long term uplift history of the massif cosmogenic data show a large variation in erosion rates marking two main domains the samples collected in the high standing low relief surface atop sila provide low erosion rates from 0 09 0 01 to 0 13 0 01 mm yr conversely high values of erosion rate up to 0 92 0 08 mm yr characterize the incised fluvial valleys on the massif flanks the analyzed river profiles exhibit a wide range of shapes diverging from the commonly accepted equilibrium concave up form generally the studied river profiles show two or more frequently three concave up segments bounded by knickpoints and characterized by different values of concavity and steepness indices the wide variation in cosmogenic erosion rates and the non equilibrated river profiles indicate that the sila landscape is in a transient state of disequilibrium in response to a strong and unsteady uplift not yet counterbalanced by erosion

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

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

geochemistry of mineralization with exchangeable rey in the weathering crusts of granitic rocks in south china abstract mineralization with exchangeable rare earth element ree and yttrium mex rey has been recognized in the weathering profiles in south china since the early 1970 s this type of rey mineralization occurs in weathering profiles of parent rocks ranging in composition from granite to acidic volcanic rocks and lamprophyre the majority of the known resources occurring in the weathering profiles of granitic rocks total resources of this type of rey amount to millions tons of rare earth oxides and therefore represent one of the most important types of rare earth resources in china particularly for heavy rare earth elements hree and yttrium accumulation of rey in the weathering profiles of granitic rocks is strongly controlled by the resistance to weathering of the principal rey bearing accessory minerals in the parent rocks only a limited proportion of total rey 4 and na etc in electrolyte solutions and can be removed by complexing agents such as edta are commonly the major form of ree occurrence in the b horizon cerium is enriched in the top layer a horizon and depleted in the subsurface horizons of the weathering profiles most likely due to the oxidation of ce iii to ce iv followed by cerianite formation or absorption onto clays and or fe and al oxyhydroxides