linking soil element mass transfer to microscale mineral weathering across a semiarid environmental gradient abstract understanding controls on silicate weathering is critical to characterizing critical zone evolution the objective of this study was to investigate how climate vegetation and landscape position control feldspar transformations across a semiarid environmental gradient granitic surface soil and saprock samples were collected from desert scrub and mixed conifer sites within the santa catalina mountain critical zone observatory where mean annual temperature ranges from 24 c to 10 c and mean annual precipitation from 25 to 85 cm quantitative x ray diffraction x ray fluorescence and electron microprobe analyses were employed to quantify elemental changes in bulk soils and across plagioclase grains the chemical depletion of na in bulk soils ranged from 5 4 15 in the desert scrub sites relative to 16 33 in the mixed conifer sites plagioclase grain alteration was classified into unaltered edge and altered sections to compare microscale weathering and elemental variation the na al and si al ratios decreased from unaltered to edge to altered grain sections in the mixed conifer sites whereas the element ratios of the desert scrub system were similar between unaltered and edge grain sections and only exhibited significant decreases in na al and si al ratios between edge and altered materials the microscale depletion of na and si suggested increased silicate weathering in the cooler wetter and more biologically productive mixed conifer system compared to the hot dry desert scrub system the results also demonstrated a topographic control on mineral transformation where increased plagioclase weathering occurred in convergent footslope landscapes with little change in elemental depletion of soils in divergent summit sites

unravelling the development of a spheroidally weathered diorite gabbro santa margarita ecological reserve peninsular ranges southern california usa abstract within santa margarita ecological reserve smer southern california an 108 ma diorite gabbro pluton has weathered spheroidally resulting in the formation of concentric rindlets i e a rindlet zone around an unaltered ellipsoidal core of the parent rock to our knowledge little is known about how spheroidal weathering is produced in mediterranean climates like that characteristic of portions of the peninsular ranges hence we undertook a detailed study aimed at determining the textural and chemical changes associated with the spheroidal weathering of the diorite gabbro pluton the parental spheroidally weathered corestone is characterized by a hypidomorphic granular texture and consists primarily of plagioclase amphibole and biotite along with minor amounts of pyroxene and quartz within the corestone sericite and uncommonly calcite and chlorite replace plagioclase the latter mineral also infrequently replaces portions of amphibole and biotite such alteration products are derived from sub solidus deuteric alteration of the pluton xrd clay mineral analysis of the 13 rindlets indicates the presence of mostly kaolinite and vermiculite and a far lesser volume of green smectite thin section study of rindlet samples suggests that vermiculite is derived from the weathering of biotite the most extensively altered mineral in the rindlet zone such alteration is paralleled by statistically significant losses of k mass across the rindlet zone in addition statistically significant losses of ca and na mass across the rindlet zone likely reflect conversion of sericite to kaolinite in contrast the absence of statistically significant losses of mg fe and mn over most of the rindlet zone implies that fluids were mostly oxidizing and that any mg leached from amphibole was likely fixed within smectite while leached fe and mn precipitated out as oxides or oxyhydroxides though calcite was present in the corestone its absence in the rindlets indicates that fluids were sufficiently acidic to dissolve and remove it previous studies have shown that spheroidal weathering occurs when volume expansion produced by a positive v of reaction builds up internal elastic strain energy in the rock for example this type of reaction occurs when iron oxidizes within biotite resulting in an expansion of d 001 from 10 a to 10 5 a or when biotite is transformed into vermiculite leading to an expansion of d 001 from 10 a to 14 a data presented here suggest that the conversion of biotite to vermiculite and the resulting positive v produced the spheroidal fracturing of the corestone at smer hence these and other data discussed in this paper suggest that the weathering of biotite is the primary driving force in the formation of spheroidally weathered corestone in the mediterranean climate of the peninsular ranges

multidisciplinary study of holocene archaeological soils in an upland mediterranean site natural versus anthropogenic environmental changes at cecita lake calabria italy abstract this paper highlights results of a multidisciplinary and multi analytical study of holocene archaeological soils around cecita lake sila massif calabria southern italy which represents a typical upland mediterranean environment it is focused on assessment of climatic and environmental changes that took place since late neolithic to roman times trying to discriminate natural from anthropogenic signals based on an integration of archaeological geomorphological stratigraphic pedological volcanological and soil charcoal pedoanthracological data the following paleoclimatic environmental reconstruction is proposed a warm and humid seasonally contrasted climate with an overall geomorphological stability suited for soil development characterized the late prehistoric environment holocene climatic optimum dominated by a widespread oak forest the main pedogenetic processes consisted in organic matter accumulation clay illuviation phyllosilicate and short range order mineral neogenesis from weathering of granite and volcanic ash sourced from late pleistocene holocene eruptions of the aeolian islands one or more mid holocene episodes of climate deterioration towards drier conditions indicated by a decrease of clay translocation processes and possible irreversible dehydration of poorly crystalline aluminosilicates into phyllosilicate clay minerals promoted intense land degradation this was in turn enhanced by increasing human activities for settlement and resource exploitation among which deforestation and ploughing for agriculture which led to a shift of the vegetation cover towards a dominant pine forest between 3 ka bp and the roman epoch humid and possibly cooler climatic conditions during the late holocene are indicated by the decrease of clay illuviation coupled with short range order components prevailing over phyllosilicate clays during roman soil formation

a spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady state denudation abstract spheroidal weathering a common mechanism that initiates the transformation of bedrock to saprolite creates concentric fractures demarcating relatively unaltered corestones and progressively more altered rindlets in the spheroidally weathering rio blanco quartz diorite puerto rico diffusion of oxygen into corestones initiates oxidation of ferrous minerals and precipitation of ferric oxides a positive v of reaction results in the build up of elastic strain energy in the rock formation of each fracture is postulated to occur when the strain energy in a layer equals the fracture surface energy the rate of spheroidal weathering is thus a function of the concentration of reactants the reaction rate the rate of transport and the mechanical properties of the rock substitution of reasonable values for the parameters involved in the model produces results consistent with the observed thickness of rindlets in the rio icacos bedrock 2 3 cm and a time interval between fractures 200 300 a based on an assumption of steady state denudation at the measured rate of 0 01 cm a averaged over times longer than this interval the rate of advance of the bedrock saprolite interface during spheroidal weathering the weathering advance rate is constant with time assuming that the oxygen concentration at the bedrock saprolite interface varies with the thickness of soil saprolite yields predictive equations for how weathering advance rate and steady state saprolite soil thickness depend upon atmospheric oxygen levels and upon denudation rate the denudation and weathering advance rates at steady state are therefore related through a condition on the concentration of porewater oxygen at the base of the saprolite in our model for spheroidal weathering of the rio blanco quartz diorite fractures occur every 250 yr ferric oxide is fully depleted over a four rindlet set in 1000 yr and saprolitization is completed in 5000 yr in the zone containing 20 rindlets spheroidal weathering thus allows weathering to keep up with the high rate of denudation by enhancing access of bedrock to reactants by fracturing coupling of denudation and weathering advance rates can also occur for the case that weathering occurs without spheroidal fractures but for the same kinetics and transport parameters the maximum rate of saprolitization achieved would be far smaller than the rate of denudation for the rio blanco system the spheroidal weathering model provides a quantitative picture of how physical and chemical processes can be coupled explicitly during bedrock alteration to soil to explain weathering advance rates that are constant in time

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

mineralogy maketh mountains granitic landscapes shaped by dissolution abstract in tectonically quiet regions the shape of the landscape is controlled by the erosion resistance of the rocks erosion largely depends on the release of particles from the weathering rock which in turn requires a degree of dissolution of the more soluble grains the rate of dissolution of the common rock forming minerals allows the construction of a numerical rock weatherability scale rws based on the rock s modal mineralogical analysis applied regionally to three granitic landscape regions of the bega valley of southern new south wales the tate batholith and featherbed volcanics of north queensland and granitoids in the beaufort region of victoria the mean elevation of the larger plutons in each region correlates highly r 0 83 0 93 with their rws variation in composition within a pluton also shows there is a clear connection between changes in rws and relief within the pluton from these results it is apparent that the landscape of such granitic terrains is determined very largely by mineral dissolution rates with plagioclase composition and content being a major factor

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

saprolite soil transformations in the piedmont and mountains of north carolina abstract in the piedmont and mountain provinces of north carolina average annual precipitation exceeds evapotranspiration soil solum thickness is usually 1 to 2 m saprolite thickness is variable but related to rock type and geomorphic position slow hydraulic conductivity in the zone between the soil and the saprolite appears to restrict vertical percolation of water thus slowing saprolite weathering on convex slopes in saprolite zones immediately above granitic gneiss often about 5 m below the surface halloysite gibbsite and x ray amorphous aluminosilicate clay are the initial secondary minerals formed halloysite contents increase upward in the saprolite apparently from resilication of gibbsite and the amorphous aluminosilicates in the upper zones of the saprolite the halloysite is recrystallized into kaolinite which is the predominant clay sized mineral in the soil over gabbro and metagabbro rocks the lower zones of the saprolite contain appreciable quantities of smectite vermiculite and where chlorite is present regularly interstratified chlorite smectite although these smectite minerals become partially interlayered with hydroxy aluminum in the overlying soil they p persist as a substantial component of the clay sized fraction saprolite thickness is less than over the granitic rocks increased run off and lateral through flow produced by low hydraulic conductives of smectite rich argillic horizons and convex hill slopes are believed to be responsible for the thin saprolite above mafic bedrock soils and saprolites from biotitic gneiss on upper sideslopes in the mountain physiographic province have mineralogical trends with depth similar to those found over the granitic gneisses of the piedmont gibbsite often constitutes as much as 30 of the clay and contents tend to increase in the deeper saprolite zones biotite sand which is common throughout the soil and saprolite alters to kaolinite sand under the acidic conditions of the saprolite sand sized mica appears resistant to weathering except where there is evidence of physical transport

elemental and strontium isotopic geochemistry of the soil profiles developed on limestone and sandstone in karstic terrain on yunnan guizhou plateau china implications for chemical weathering and parent materials abstract the limestone and yellow sandstone soil profiles from sw china were measured for chemical and sr isotope compositions of the bulk soils and their sequential leachates labile carbonate and residue or silicate fraction aiming to characterize the parent materials of the soils to understand the soil weathering and formation processes and to discuss the origin of the red residua terra rossa the studied yellow sandstone soil yellow limestone soil and black limestone soil show different ph values sio 2 contents rb sr abundance ratios and 87 sr 86 sr ratios the sequential leachates of different soil types also have different 87 sr 86 sr and ca sr ratios the major chemical compositions of the studied soil profiles suggest that all the sandstone and limestone soils are developing at a stage that feldspar is exhausting and the clay minerals are changing from smectite to kaolinite and gibbsite as compared with the red residua distributed in the karst region the soils studied here show lower cia values 58 84 but both higher na 2 o k 2 o 0 9 2 7 and na 2 o al 2 o 3 concentration ratios 0 07 0 26 on average suggesting a lower weathering intensity than that of the red residua the depth profiles of soil cia values na 2 o k 2 o and rb sr ratios and 87 sr 86 sr ratios indicate that the weathering intensity is slightly lower for the upper and higher for the deeper soils which suggest that the sandstone and limestone soil profiles were formed through both accumulation and weathering of in situ weathering residue and input of external detritus or soil from upper land during weathering of the soils preferential release of ca and retention of sr in soil result in higher ca sr ratios in both labile and carbonate fractions than those in the residue fractions of all soil profiles the co variations of hf nb and zr nb ratios together with those rb sr and 87 sr 86 sr ratios of limestone soils sandstone soils and the red residua demonstrate that their parent materials are distinct and support the point that the widely distributed red residua is originated from the weathering residua of both carbonate and silicate clastic rocks and further weathering of the weathering residua resulted in intensive release of si na ca and relative enrichment of al k and other immobile elements in the red residua

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

effect of granite crystal grain size on soil properties and pedogenic processes along a lithosequence this study generated new insight into the effect of bedrock grain sizes on pedogenesis under identical topographic and climatic environment the physico chemical and mineralogical properties of two adjacent typic dystrochrepts usda 1999 respectively developed from fine and coarse textured granites were compared this research study was performed in the morvan mountains france analysis of the two underlying bedrocks revealed similar chemical and mineralogical properties with the crystal grain size being the only parameter which differed in these soils bedrock played the key role in the particle size fraction distribution the main factor controlling water retention in the soils weathering reactions of clay minerals were more marked in the fine textured granite soil in this soil both clay mineral swelling and mica transformation into expansible phyllosilicates were greater compared to the coarse textured granite soil in the clay fraction of the fine textured granite soil there were smaller amounts of low crystallised fe and al minerals with higher carbon content in the topsoil as compared to the coarse granite soil the exchangeable cation analysis of the fine textured granite soil revealed a higher proportion of base saturation and a smaller proportion of altit than in coarse textured granite soil which could be explained by preferential leaching of al cations the decrease in exchangeable al the higher swelling of the smectitic layer and the smaller proportion of fe and al oxy hydroxides could be explained by the complexing acid conditions which increased mineral weathering and al leaching the higher water retention increased the time of contact between minerals and the soil solution and the higher carbon content in the topsoil could have enhanced the complexing acid conditions resume d auteur

stratification and mixing of a post glacial neoproterozoic ocean evidence from carbon and sulfur isotopes in a cap dolostone from northwest china abstract to improve our knowledge about the geochemical and environmental aftermath of neoproterozoic global glaciations we analyzed stable isotopes 13 c 18 o 34 s and elemental concentrations ca mg s sr fe and mn of the 10 m thick zhamoketi cap dolostone atop the tereeken diamictite in the quruqtagh area eastern chinese tianshan available chemostratigraphic data suggest that the tereeken diamictite is probably equivalent to the marinoan glaciation our new data indicate that organic and carbonate carbon isotopes of the zhamoketi cap dolostone show little stratigraphic variations averaging 28 2 and 4 6 respectively in contrast sulfur isotopes show significant stratigraphic variations carbonate associated sulfate cas abundance decreases rapidly in the basal cap dolostone and 34 s cas composition varies between 9 and 15 in the lower 2 5 m in the overlying interval cas abundance remains low while 34 s cas rises 5 and varies more widely between 10 and 21 the range of 34 s py of the cap dolostone overlaps with that of 34 s cas but direct comparison shows that 34 s py is typically greater than 34 s cas measured from the same samples hypotheses to explain the observations must account for both the remarkable sulfur isotope enrichment of pyrites and the inverse fractionation we propose that cas and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin or a basin with a sulfate minimum zone in this model cas was derived from shallow oxic surface waters with moderate sulfate concentration and depleted in 34 s due to the post glacial influx of sulfur from continental weathering in contrast pyrite was derived from anoxic bottom waters or a sulfate minimum zone with low sulfate concentration and 34 s enrichment due to long term syn glacial sulfate reduction the rapid shift in cas abundance and sulfur isotope composition within the cap dolostone is interpreted to reflect the mixing of the two reservoirs after initial deglaciation comparison with other post marinoan cap carbonates shows significant spatial heterogeneity in 34 s cas which together with strong temporal variation in 34 s cas points to generally low sulfate concentrations in post marinoan oceans

lithological effects in soil formation and soil slips on weathering limited slopes underlain by granitic bedrocks in japan abstract soil slips occur every few years due to heavy rains on biotite granite gb and hornblende biotite granite ghb slopes in the taga mountains ibaraki prefecture japan the occurrence density of soil slips per unit area is 2 7 times greater in the gb slopes than that in ghb slopes we examined the chemical mineral physical and mechanical properties of two soil profiles on soil slip scars in these slopes to study the effect of bedrock mineral composition on the density of soil slips for a given size of mineral grain the amount of biotite which is susceptible to chemical weathering in granitic bedrocks strongly influenced the density of soil slips in the gb slope the soil layer becomes thinner because of the smaller proportion of biotite in the bedrock this restricts the downward movement of soil water into the material below the slip plane during heavy rainfall the water surface then rises toward the slope surface above the slip plane this promotes soil slips increasing the density of soil slip scars in contrast in the ghb slope with more biotite in the bedrock the soil layer becomes thicker so that soil water moves easily into the material beneath the slip plane this limits the rise of water surface toward the slope surface above the slip plane even during heavy rainfalls there are consequently fewer soil slips and density of soil slip scars

effects of slope orientation on pedogenesis of altimontane soils from the brazilian semi arid region baturite massif ceara given the importance of climate conditions for the development of soils studies on climosequences are a valuable tool to predict the influence of climate change on weathering rates and on soil formation processes the baturite massif a humid enclave located in the brazilian semi arid region has unique characteristics that cause a disproportional distribution of rainfall the eastern and northern slopes receive more than 1 600 mm year of rainfall whereas the southern and western slopes have semi arid characteristics with rainfall of less than 600 mm year eight soil profiles were selected to investigate the influence of these distinct climates on soil formation to achieve this physical chemical morphological mineralogical and micromorphological data were determined and analyzed in the humid slope predominate soil processes include melanization brunification intense leaching acidification and alitization with intensified weathering in higher altitudes in contrast the environment in the dry slope favored the occurrence of soils with a higher base status high activity clays low al saturation and bisialitization processes coexisting with monosialitization mainly in the soils located at lower altitudes micromorphological data indicate that clay illuviation is not the main process responsible for the enrichment of clay in the subsurface horizons the contrasting environmental conditions with different mineralogical composition seem to be an important indicator of weathering intensity and pedoenvironmental conditions

weathering of granites in a temperate climate nw portugal granitic saprolites and arenization abstract saprolites or in situ weathering products from granitoid rocks of northwest portugal were studied by means of x ray diffraction xrd of their clay fraction and observations of polished thin sections combined with transmission electron microscopy tem scanning electron microscopy with energy dispersive spectrometer sem eds microanalyses their principal features are 1 depths of more than 10 m 2 mean material loss of 40 as calculated by an isovolumetric method 3 low clay content mean value of 7 and a high degree of mineralogical evolution the clay fraction is characterized by a predominance of kaolinite and gibbsite with subordinate 2 1 minerals illite chlorite vermiculitic mixed layers vermiculite the significance of the secondary minerals in granitic saprolites from northwest portugal is compared to published data from atlantic europe this allows the definition of a climatic zonality for weathering products and identifies arenization as an important weathering process

application of laser ablation icp ms and traditional micromorphological techniques to the study of an alfisol sardinia italy in thin sections insights into trace element distribution abstract an innovative methodological approach is proposed in this study based on the chemical analysis of different portions of soil horizons illuvial pedofeatures pedogenic matrix and skeletal parent rock fragments by laser ablation inductively coupled plasma mass spectrometry la icp ms associated with traditional micromorphological optical and scanning electron microscopy techniques validation of the la icp ms technique provides in situ accurate and reproducible rsd 13 18 analysis of low concentration trace elements and rare earth elements ree in soil samples 0 001 0 1 ppm analyses were carried out on thin sections prepared from undisturbed soil samples collected from three different bt argillic i e clay illuviated horizons in an alfisol from the muravera area southeastern sardinia italy the main aims were i to develop and test the reliability of a la icp ms analytical method on soil thin sections and ii to explore the idea that concentrations of trace and rare earth elements in the different portions of a soil profile can be used to investigate their distribution as a response to pedogenetic processes the three horizons show similar features particularly in terms of element concentrations and patterns by comparing the concentration of ree and other trace elements in the clay coatings the soil matrix and the skeletal rock fragments in the same horizon a general enrichment trend is observed from the parent rock to the pedogenic matrix up to the illuvial pedofeatures suggesting a prominent role of pedogenetic processes in element fractionation and distribution during weathering in particular the highest concentration of trace elements and specifically ree in clay coatings which represent the most mobile solid phase in the soil profile indicates that the former can be used as a reliable indicator of soil weathering if a preliminary assessment of the presence of clay coatings is achieved in addition the discontinuous trend of some trace elements among soil features of different horizons is consistent with field evidence of slope dynamics marked by an erosive and depositional discontinuity along the soil profile

deep weathering of granitic rocks a case of tunnelling in nw spain abstract this paper highlights a case of extensive development of saprolith from granitic bedrock in nw spain the weathering front at the study area extends to more than 250 m in depth the drilling of a railway tunnel madrid galicia high speed line through the bedrock and saprolith resulted in significant technical issues and economic losses cross sections revealing the 3d complexity of saprolith development are mainly based on fieldwork boreholes laboratory tests and the excavation works saprock is always observed overlying unweathered igneous bedrock two saprolite facies one clay rich and the other clay poor overlie the saprock the recognition is based on several criteria these deposits gradually thicken from the boundaries between the granitoid and metasedimentary roof pendants factors controlling saprolith development are discussed and the chemical and mineralogical changes and trends that occur are described variations in some geotechnical properties and the loss of quality of the rock masses from an engineering perspective are also quantified

weathering profiles in granitoid rocks of the sila massif uplands calabria southern italy new insights into their formation processes and rates abstract in this paper we characterized several weathering profiles developed on granitoid rocks in the sila massif upland calabria southern italy integrating detailed macro and micromorphological observations with physico mechanical field tests and petrographic mineralogical and geochemical analyses we focused our attention on the main weathering and pedogenetic processes trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties and two common weathering indices such as the micropetrographic index ip and the chemical index of alteration cia our results showed that sericite on plagioclase and biotite chloritization that represent inherited features formed during late stage hydrothermal alteration of granitoid rocks may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions especially in lower weathering grade classes moreover the frequent identification of fe mn oxides and clay coatings of illuvial origin rather than or in addition to those formed in situ both at the macro and microscale may also explain an overestimation of the weathering degree with respect to field based classifications finally some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes cryoclastism and thermoclastism that lead to rock breakdown even when chemical weathering is not well developed hence our study showed that particular caution is needed for evaluating weathering grades because traditional field and geochemical petrographic tools may be biased by inherited hydrothermal alteration physical weathering and illuvial processes on the basis of chronological constraints to soil formation obtained from a 42 ka old volcanic input mixed to granite parent materials detected in the soil cover of the sila massif upland a first attempt to estimate soil formation rates was achieved for different depths of corresponding weathering profile zones soil formation rates ranged from 0 01 0 07 mm a 1 for a and bw horizons weathering class vi to 0 04 0 36 mm a 1 for the underlying saprolite c and cr layers class v by comparing these results with the corresponding erosion rates available in the literature for the study area that range from

weathering and pedogenesis in the sila grande massif calabria south italy from field scale to micromorphology abstract weathering and soil features in the upland landscapes developed on granitic terrains of the sila grande massif calabria south italy have been studied in this work the attempt to link field scale and micromorphological observations in order to better understand the main weathering processes and their controlling factors is revealed to be very powerful six soil profiles in the area around the cecita lake representative of different geomorphological units were characterised by field work optical microscopy and sem eds analysis a strong influence on weathering and pedogenesis by micro scale features of primary minerals and parent rock fabrics is shown key roles are played also by relief in the development and preservation or stripping of regolith soil mantles in relation to natural and man induced phenomena by time controlling rates and degree of development of the main weathering features by climate in terms of type and intensity of dominant processes

deep weathering along a granite ridgeline in a subtropical climate abstract bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11 meter profile weathering on a granite ridgeline under subtropical climate conditions in south china the weathering sequence is delineated by mineralogy and major element variations apatite biotite hornblende and plagioclase dissolve early during weathering resulting in nearly 100 ca and na loss and significant mg fe and p depletion at depth the k feldspar reaction front begins at the depth of depletion of plagioclase leading to a loss of 80 of the k at the land surface near the bottom of the ridgeline and almost 100 at the top dissolution of quartz and other silicates releases about 60 of si in the profiles kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer the soil horizon upper 100 cm is the zone dominated by pedogenic processes including active biological activity physical erosion and influx of high concentrations of atmospheric components especially co2 and o2 the pedogenic processes are characterized by low ph 4 54 to 5 85 high clay content kaolinite 6 16 wt gibbsite 2 8 wt and total organic carbon content 0 13 3 93 and intensive fracturing and dissolution of quartz and k feldspar compared with the lower horizons accumulation of organic material and resistant minerals downslope is attributed to down ridge movement of water termed here interflow and weathering products in the uppermost 100 cm down the ridgeline using a mass balance model calculation for the catena that assumes steady state soil thickness at all sites the bottom profile shows the highest apparent total chemical weathering loss rate 14 g m 2 y 1 whereas the middle position shows the highest physical erosion loss rate 44 g m 2 y 1 sio2 accounts for about 84 of the chemical weathering outflux from the soil horizons along the ridgeline hillslope chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite this study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena

geochemical features of rocks stream sediments and soils of the fiume grande valley calabria italy the role of both natural weathering and anthropogenic pollution in controlling the distribution of major oxides and several trace elements in soils stream sediments and rocks of the fiume grande catchment was evaluated the contents of major oxides and trace elements in soils appear to be governed by weathering and pedogenetic processes although the use of fertilizers in agriculture could also partly affect k2o and p2o5 contents stream sediments have concentrations of major oxides except cao very similar to soils as relevant amounts of soil materials are supplied to the stream channels by erosive phenomena in contrast stream sediments have concentrations of cr co ni zn as and pb significantly higher than those of soils probably due to different conditions and rates of mobility of these elements within the three considered matrices and or disposal of wastes in the drainage network comparison of the concentrations of phes in soils with the maximum admissible contents established by the italian law shows that these limits are too restrictive in some cases and too permissive in other ones the approach of setting these limits with no consideration for the local geological geochemical framework may lead to improper management of the territory and its resources

retracking ers 1 altimeter waveforms for optimal gravity field recovery summary we have reprocessed ers 1 radar altimeter waveforms using an algorithm designed to minimize sea surface slope error and decouple it from significant wave height swh error standard waveform retracking estimates three parameters arrival time swh and amplitude we show that errors in retracked estimates of arrival time and swh are inherently correlated because of the noise characteristics of the returned waveform this suggests that some of what is called sea state bias in the literature may be caused by correlated errors rather than true electromagnetic or skewness bias we have developed a retracking algorithm that reduces this error correlation and makes the resolution of sea surface slope signals independent of sea state the main assumption is that the swh varies smoothly along the satellite track over wavelengths of 90 km this approach reduces the rms error in sea surface slope to only 62 per cent of that of standard retracking methods while our method is optimized for gravity field recovery it may also improve the resolution of sea surface height signals of interest to physical oceanographers