syndeformational fluid trapping in quartz determining the pressure temperature conditions of deformation from fluid inclusions and the formation of pure co2fluid inclusions during grain boundary migration observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids our results imply that pure co2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation recrystallization process rather than representing a primary metamorphic fluid where the temperature of deformation can be deduced by other means the densities of fluid inclusions trapped during recrystallization which we call recrystallization primary fluid inclusions can be used to constrain the ambient pressure during deformation using these constraints the data imply that the post metamorphic hercynian exhumation in sardinia brought rocks at 300 c to within 3km of the surface this conclusion is similar to that described for the rapidly uplifted southern alps in new zealand

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

spatial variability in bank resistance to erosion on a large meandering mixed bedrock alluvial river abstract spatial heterogeneity in the erosion resistance properties of the channel banks and floodplains associated with sediment characteristics vegetation or bedrock can have a substantial influence on the morphodynamics of meandering rivers resulting in highly variable rates of bank erosion and complex patterns of planform evolution although past studies have examined the spatial variability in bank erodibility within small rivers this aspect of the erosion resistance properties for large rivers remains poorly understood furthermore with the exception of recent numerical modeling that incorporates stochastic variability of floodplain erosional resistance most models of meandering river dynamics have assumed uniform erodibility of the bank and floodplain materials the present paper investigates the lateral and vertical heterogeneity in bank material properties and riparian vegetation within two elongate meander loops on a large mixed bedrock alluvial river using several geotechnical field and laboratory methods additionally the bank stability and toe erosion numerical model bstem and repeat terrestrial lidar surveys are used to evaluate the capacity of the bank material properties to modify the rates and mechanisms of bank retreat results show that the textural properties of the bank materials soil cohesion and critical shear stress necessary for sediment entrainment differ substantially between the two bends and are also highly variable within each bend laterally and vertically trees growing along the banks increase the resistance to erosion by contributing to the shear strength of the bank materials and are capable of increasing bank stability along a large river locally outcropping bedrock also influences bank erodibility in both bends the results of this study demonstrate that spatial variability in the erosion resistance properties of the channel banks is an important factor contributing to spatial variability in the rates and mechanisms of bank erosion determined from short term studies of bank retreat and long term analysis of changes in channel planform

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

synmetamorphic high density carbonic fluids in the lower crust evidence from the nilgiri granulites southern india high density co2 inclusions occur abundantly in granulite facies rocks age of metamorphism approximately 2 5 b y of the nilgiri massif southern india the chronology of carbonic inclusions in the widespread enderbitic granulites studied in relation to the development of micro textures and mineral assemblages indicates that randomly oriented negative crystal shaped co2 inclusions 4 20 mu m in garnet and quartz grains qtz i armoured by garnet entrap syn peak metamorphic pore fluids the more abundant trail bound co2 inclusions in the deformed polygonized and partially recrystallized matrix quartz grains qtz ii and iii and plagioclase grains were formed in connection with a stage of compressional deformation and subsequent annealing related to the development of the late proterozoic bhavani shear zone these inclusions resulted from local re equilibration of the former peak granulitic carbonic inclusions and re entrapment of released fluids the presence of pure co2 in all the inclusions is confirmed by microthermometric data and laser excited raman microspectrometry temperatures of homogenization liquid phase are in the range of 50 to 20 degrees c and the corresponding co2 densities are between 1 154 and 0 807 g cm3 mineralogical thermobarometry on the enderbitic granulites documents a continuous gradient of near peak metamorphic conditions from 750 degrees c 9 10 kb in the northern part to 730 degrees c 7 kb in the southwestern part of the nilgiri massif uniform p t estimates 600 650 degrees c 6 7 kb for late coronitic garnet quartz assemblages in enderbites and metadolerites indicate that differential uplift of the massif to mid crustal levels was accomplished before late compressional deformation in conformity carbonic inclusions in quartz ii and iii are characterized by uniformly high density 1 154 1 08 g cm3 in contrast early carbonic inclusions in garnet and quartz i preserve the density contrast reflecting the regional p t gradient during near peak metamorphic fluid entrapment the fluid inclusion systematics indicate near isochoric uplift of the northern high p domain but near isobaric cooling of the southwestern low p domain the carbonic fluids are thought to have been derived either from internal sources during dehydration melting processes or from freezing synmetamorphic intrusives into the lower crust

modeling the evolution of incised streams ii streambank erosion incision and ensuing widening of alluvial stream channels is widespread in the midsouth and midwestern united states and represents an important form of channel adjustment streambanks have been found to contribute as much as 80 of the total suspended load the location timing and magnitude of streambank erosion are difficult to predict results from field studies to characterize the resistance of fine grained materials to hydraulic and geotechnical erosion the impact of pore water pressures on failure dimensions and shearing resistance and the role of riparian vegetation on matric suction streambank permeability and shearing resistance are used to enhance the channel evolution model concepts conservational channel evolution and pollutant transport system this paper discusses the conceptualization of the above mentioned physical processes and demonstrates the ability of the derived model to simulate streambank failure processes the model is tested against observed streambank erosion of a bendway on goodwin creek miss between march 1996 and march 2001 where it accurately predicts the rate of retreat of the outside bank of the bendway the observed change in average channel width within the central section of the bendway is 2 96 m over the simulation period whereas a retreat of 3 18 m 7 4 larger is simulated the observed top bank retreat within the central section of the bendway is 3 54 m over the simulation period whereas a retreat of 3 01 m 15 smaller is simulated doi 10 1061 asce0733 94292008134 7905 ce database subject headings bank erosion limit equilibrium mathematical models sensitivity analysis numerical analysis

reply to the discussion by denis lacelle on the biogenic origin of needle fibre calcite by cailleau et al 2009 sedimentology 56 1858 1875

extremely high density pure co2 fluid inclusions in a garnet granulite from southern india abstract a late archean 2 4 2 7 ga garnet granulite from the southern margin of the south indian craton preserves fluid inclusions with the highest density co2 yet reported from lower crustal rocks the rock comprises garnet clinopyroxene salite plagioclase amphibole pargasite orthopyroxene hypersthene biotite scapolite and quartz with accessory k feldspar ilmenite apatite and ankerite pressure temperature estimates of 9 11 kbar and 740 800 c are computed from electron microprobe data on equilibrium assemblages we report here detailed inclusion petrography and microthermometric data on fluids trapped in garnet feldspar and quartz from the granulite the dominant category in all these minerals are composed of monophase carbonic inclusions with melting temperatures close to 56 6 c indicating a co2 rich composition for the fluid laser raman microscopic studies confirm that the fluid is pure co2 with no traces of impurities such as n2 and or ch4 the inclusions homogenize into the l

microbial origin for pedogenic micrite associated with a carbonate paleosol champagne france abstract micro rods have been observed in indurated carbonate horizons 30 cm thick that overlie a periglacial chalk formation in contact with the present day soil champagne france they are numerous in the upper part of the hardened layers variations in micro rod morphologies are related to progressive biomineralization of organic matter transforming purely organic rods into calcite mineralized rods undergo diagenesis and their arrangement evolves from a random mesh fabric to recrystallized micritic platelets to microsparite two types of organic micro rods have been observed bacilliform and thread like bacteria mineralogically micro rods are low magnesian calcite crystallographically their length is parallel to the 104 axis and they grow along the 010 plane micro rods can be associated with needle fiber calcite they increase the caco3 content of the primary matrix and infill its microporosity their diagenetic evolution into microsparite contributes to soil layer induration

vertical variation in porosity of nāri calcrete on chalk galilee israel a new interpretation as a tribute to dan h yaalon abstract n ri calcrete is a calcareous formation common in the semiarid mediterranean region of the levant the profile studied in nazareth galilee is 2 75 m thick and divided into the four conventional layers i e a chalky bedrock a powdery lower n ri an indurated and platy upper n ri and a laminar crust capping the profile in this study mercury intrusion porosimetry mip is used to assess the genetic processes at work in the formation of n ri calcrete based on the former work by yaalon and singer 1974 and mip results various parameters are proposed to describe the different layers total porosity n p trapped porosity n t permeability k and strength c these parameters are compared to each other for each layer as well as with their respective calcium carbonate contents an unexpected relationship shows that the more caco 3 is present the more porous the layer of the n ri consequently the lower n ri is interpreted as a weathering layer of the parent chalk whereas the upper n ri which is the most porous and the richest in caco 3 results from in situ recrystallization the upper n ri permeability precludes it from playing the role of a plugged horizon to explain the formation of the laminar crust in conclusion the n ri calcrete in nazareth questions the conventional model of calcrete genesis as its cementation is due to in situ redistribution of caco 3 rather than its translocation these results strengthen yaalon and singer 1974 s conclusions

dehydration melting and the granulite transition in metapelites from southern namaqualand s africa in a prograde amphibolite granulite transition zone in the namaqualand metamorphic complex metapelites show an interbanding of the amphibolite facies association biotite sillimanite quartz with the granulite facies association garnet cordierite k feldspar relict graded bedding shows that compositional banding is of sedimentary origin the garnet cordierite k feldspar gneisses contain quartzofeldspathic segregations surrounding garnets and have more fe rich bulk compositions than the biotite sillimanite schists

bank erosion processes in regulated navigable rivers vessel induced waves affect the morphology and ecology of banks and shorelines around the world in rivers used as waterways ship passages contribute to the erosion of unprotected banks but their short and long term impacts remain unclear this work investigates the effects of navigation on bank erosion along a reach of the regulated meuse river with recently renaturalized banks we apply uav sfm photogrammetry rtk gps acoustic doppler velocimetry aerial and terrestrial photography soil tests and multibeam echosounding to analyze the progression of bank retreat after riprap removal after having analyzed the effects of ship generated waves and currents floods and vegetation dynamics a process based model is proposed to estimate the long term bank retreat the results show that a terrace evolves in length and depth across the bank according to local lithology which we clustered in three types floods contribute to upper bank erosion inducing mass failures while near bank flow appears increasingly ineffective to remove the failed material due to terrace elongation vegetation growth at the upper bank toe reduces bank failure and delays erosion but its permanence is limited by terrace stability and efficiency to dissipate waves the results also indicate that long term bank retreat is controlled by deep primary waves acting like bores over the terrace understanding the underlying drivers of bank evolution can support process based management to optimize the benefits of structural and functional diversity in navigable rivers

origin of strontium and calcium in pedogenic needle fibre calcite nfc abstract strontium sr and calcium ca isotopic compositions and sr ca ratios have been analysed in different fractions of pedogenic needle fibre calcite nfc from the swiss jura mountains villiers neuch tel switzerland in order to determine their ca sources and to investigate the potential role of fungi in the origin of nfc 87sr 86sr ratios have been measured to trace the ca trapped within different pedogenic carbonate this ratio was compared for previously identified microscopic morphological groups of nfc the bulk soil fine earth

a physically based model to predict hydraulic erosion of fine grained riverbanks the role of form roughness in limiting erosion hydraulic erosion of bank toe materials is the dominant factor controlling the long term rate of riverbank retreat in principle hydraulic bank erosion can be quantified using an excess shear stress model but difficulties in estimating input parameters seriously inhibit the predictive accuracy of this approach herein a combination of analytical modeling and novel field measurement techniques is employed to improve the parameterization of an excess shear stress model as applied to the lower mekong river boundary shear stress is estimated using a model kean and smith 2006a 2006b for flow over the irregular bank topography that is characteristic of fine grained riverbanks bank erodibility parameters were obtained using a cohesive strength meter tolhurst et al 1999 the new model was used to estimate annual bank erosion rates via integration across the mekong s annual flow regime importantly the simulations represent the first predictions of hydraulic bank erosion that do not require recourse to calibration thereby providing a stronger physical basis for the simulation of bank erosion model predictions as evaluated by comparing simulated annual rates of bank toe retreat with estimates of bank retreat derived from analysis of aerial photographs and satellite imagery indicate a tendency to overpredict erosion root mean square error equals 0 53 m yr form roughness induced by bank topographic features is shown to be a major component 61 85 of the spatially averaged total shear stress and as such it can be viewed as an important factor that self limits bank erosion

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

fluid evolution and exhumation path of the trivandrum granulite block southern india in charnockites and host garnet biotite gneis ses of the trivandrum granulite block tgb southern india fluid inclusions are mainly represented by co2 rich categories aqueous inclusions with low salt concentration 0 33 13 5 wt nacl equiv occur sub ordinately we recognize three generations of co2 rich inclusions which have contrasting fluid densities that correlate with the different stages of metamorphic evo lution established from mineral phase equilibria studies although some of these inclusions show variable depression in melting temperatures laser raman spec troscopic studies revealed no volatiles other than co2 we report here the occurrence of high density co2 rich inclusions for the first time from this region with homogenization temperatures in the range of 21 9 to 15 6 c q 1 041 1 012 g cm 3 the marked secondary character of these high density inclusions and their tex tural association with late brittle deformational features indicate their entrapment at low temperature conditions 250 300 c post dating charnockite formation regional metamorphism in tgb stage m1 took place at ca 700 c and 5 36 kbar although higher tempera tures prevailed in the northern part of the terrain a subsequent period of decompression of the order of 6 7 km was accompanied by partial recrystallization of host rocks and intensive processes of charnockite for mation m2 that extended to subisobaric cooling from 785 805 to 680 700 c the relatively small population of aqueous inclusions in charnockites and their low salinity preclude any major role for metasomatic pro cesses involving increase of potassium activity and confirm the important role of co2 rich fluids in stabi lizing low water activities during the final phase of exhumation of the region ca 9 km in depth additional heat input resulted in mineralogical alterations corre lated to stage m3 while the source of heat and fluids involved in charnockite formation is postulated to be magmas derived from sublithospheric sources the late heat and fluid transfer are correlated to late pan african ultrabasic and alkaline intrusives emplaced at shallow depths

small scale secondary caco3 accumulations in selected sections of the european loess belt morphological forms and potential for paleoenvironmental reconstruction eighteen important quaternary loess paleosoil sites have been studied across the european loess belt they included approximately 50 buried soils the over and or underlying loess and the present day surface soils where possible from the numerous types of secondary caco3 accumulations recognized only the small scale accumulations are discussed in this paper including calcified root cells caco3 hypocoatings needle fiber calcite powdery calcite coatings earthworm biospheroliths and calcite pseudomorphs on gypsum most of the features studied are found in the rhizosphere microecosystem each of these features showed a unique relationship with organic matter micro organism and plant distribution moisture and leaching processes for example the exceptional abundance of calcified root cells is an indicator of a long stability of soil surface during favorable climatic conditions needle fiber calcite is related to biomineralization of saprophytes in soils with sufficient moisture and decomposing organic matter the presence of powdery calcite coatings covering clay and mn coatings in non calcareous soils indicates a change from leaching to non leaching soil moisture regimes earthworm biospheroids provide arguments for a relative stability of the soil surface without rapid burial processes or drastic prolonged water stress finally gypsum pseudomorphs are indicators of changes in local climatic parameters in addition to a discussion of the genesis and the dynamics of the various accumulations several examples are given to show how these accumulations can be used as indicators of a changing environment such as renewed loess deposition the extent of drought or varying intensity of leaching during the year to conclude various forms of small scale secondary caco3 accumulations are common in the loess paleosoils and each type has the potential to contribute to a better understanding of the evolution of the paleoenvironment therefore it is proposed that their individual presence or absence throughout the pedostratigraphical levels and throughout the paleo topography should be recorded at all scales of observation

alkaline magmatism versus collision tectonics in the eastern ghats belt india constraints from structural studies in the koraput complex abstract linear domains of deformed alkaline rocks and carbonatites have recently been identified as representing sites of ancient suture zones in peninsular india the western margin of the proterozoic eastern ghats belt egb is characterized by a series of alkaline plutons that are aligned close to the contact with the archaean craton most of the complexes were deformed and metamorphosed during a subsequent orogenic event unlike other plutons in the belt the alkaline complex at koraput reportedly escaped deformation and granulite facies metamorphism forming an anomalous entity within the zone multiply deformed country rocks hosting this complex underwent syn d1cr granulite facies metamorphism followed by d2cr thrusting with pervasive shearing along a ne sw trending foliation a second granulite facies event followed localized d3cr shearing within the koraput complex strain partitioning was responsible for preserving igneous textures in the gabbroic core but aligned magmatic amphibole needles and plagioclase laths occasionally define a s1ac fabric along the margins s1ac is rotated parallel to a ne trending east dipping s2ac fabric in the gabbro fringing syenodiorite and nepheline syenite bands locally d3ac shearing follows d2ac deformation s2ac and s3ac parallel s2cr and s3cr in the country rocks high grade metamorphism represented by recrystallization of amphibole and plagioclase and breakdown of amphibole and biotite to garnet pyroxene and k feldspar in the complex follows d3ac unlike earlier reports therefore the koraput body is also deformed and metamorphosed the aligned alkaline complexes in the egb probably represent deformed alkaline rocks and carbonatites formed by rifting related to an earlier episode of continental break up that were deformed during subsequent juxtaposition of the egb with the archaean craton this supports the contention that the western margin of the egb and its contact with the archaean craton is a suture zone related to the indo antarctica collision event

how long lived is ultrahigh temperature uht metamorphism constraints from zircon and monazite geochronology in the eastern ghats orogenic belt india abstract along the coast of peninsular india the eastern ghats expose a deep crustal section through a composite proterozoic orogenic belt to quantify the late mesoproterozoic early neoproterozoic pressure p temperature t time t evolution of the eastern ghats province new shrimp u pb zircon and monazite age data from multiple localities are reported and integrated with the results of phase equilibria modelling samples of residual granulite migmatite and enderbite yield a spread of weighted mean 207pb 206pb zircon and monazite ages between ca 970 and ca 930 ma based on ranges of spot ages from several samples the late prograde to peak ultrahigh temperature uht metamorphism counter clockwise evolution ccw to t 950 c at p 8 kbar and initial cooling is interpreted to have occurred between ca 1130 and ca 970 ma regionally extensive enderbite and charnockite magmas were emplaced into the hot suprasolidus crust around the time of peak metamorphism for the residual granulites and migmatites the retrograde p t t path is characterized by close to isobaric cooling to the variable but elevated solidi for different samples weighted mean ages between ca 970 and ca 930 ma in several samples are interpreted to record the timing of crystallization of melt trapped by the percolation threshold in each of these samples two additional weighted mean ages of ca 980 ma from korhonen f j saw a k clark c brown m bhattacharya s 2011 new constraints on uht metamorphism in the eastern ghats province through the application of phase equilibria modelling and in situ geochronology gondwana research 20 764 781 extend this range back in time by 10 my the variability in the calculated weighted mean ages across the region is interpreted to be due mainly to differences in the temperature of the elevated solidus from sample to sample suggesting a slow cooling rate of 1 c my during the retrograde stage of this long lived uht metamorphism these results demonstrate that the eastern ghats province sustained uht conditions t 900 c for 50 my and perhaps for as long as 200 ma from ca 1130 to 930 ma during a single ccw tectono metamorphic event

modeling the evolution of incised streams i model formulation and validation of flow and streambed evolution components a robust computational model for simulating the long term evolution of incised and restored or rehabilitated stream corridors is presented the physically based model simulates the three main processes that shape incised streams hydraulics sediment transport and streambed and bank adjustments a generalized implicit preissmann scheme is used for the spatial and temporal discretization of the flow governing equations to accommodate large time steps and cross sections spaced at irregular intervals the solution method introduces several enhancements that increase its robustness specifically to simulate flashy flows transport of cohesive or cohesionless graded bed material is based on a total load concept and suspended and bed load transport modes are accounted for through nonequilibrium effects the model simulates channel width adjustment by hydraulic erosion and gravitational mass failure of heterogeneous bank material the present paper focuses mainly on the treatment of streamflow hydraulics and evolution of graded streambeds and reports simulations of published experiments on degrading and aggrading channels with graded bed material description and validation of the model s stream bank erosion component and the application of the model to incised stream systems are presented elsewhere

numerical simulations of co2 migration during charnockite genesis charnockite is considered to be generated either through the dehydration of granitic magma by co2 purging or by solid state dehydration through co2 metasomatism during granulite facies metamorphism to understand the extent of dehydration co2 migration is quantitatively modeled in silicate melt and metasomatic fluid as a function of temperature h2o wt pressure basal co2 flux and dynamic viscosity numerical simulations show that co2 advection through porous and permeable high grade metamorphic rocks can generate dehydrated patches close to the co2 flow path as illustrated by the occurrences of incipient charnockites co2 reaction front velocity constrained by field observations is 0 69 km m y a reasonable value which matches well with other studies on the other hand temperature rate of cooling and basal co2 flux are the critical parameters affecting co2 diffusion through a silicate melt co2 diffusion through silicate melt can only occur at temperature greater than 840 degrees c and during slow cooling 3 7 x 10 5 degrees c yr features that are typical of magma emplacement in the lower crust stalling of co2 fluxing at similar to 840 degrees c explains why some deep level plutons contain both hydrous and anhydrous charnockitic mineral assemblages co2 diffusion through silicate melt is virtually insensitive to pressure addition of co2 basal flux facilitates episodic dehydrated melt migration by generating fracture pathways

co 2 melts and granulite metamorphism the discovery that granulites contain co2 rich fluid inclusions while amphibolites in the same terrane contain h2o rich or mixed co2 h2o inclusions1 has led to a debate over the processes that produce granulite metamorphism one theory2 4 maintains that granulites form as the result of a massive influx of co2 from lower crustal or mantle sources such an influx could be responsible for the marked depletion many granulite terranes show in large ion lithophile elements2 5 others however maintain that granulite facies metamorphism is a necessary complement of crustal melt ing6 9 recently lamb and valley10 11 have argued that granulite metamorphism may be a product of any one of three processes co2 streaming partial melting or recrystallization of originally dry rocks here we suggest that these processes need not be independent and that they all may be related to the passage of melts through the crust

origin of abundant moonmilk deposits in a subsurface granitic environment subsurface granitic environments are scarce and poorly investigated a multi disciplinary approach was used to characterize the abundant moonmilk deposits and associated microbial communities coating the granite walls of the 16th century paranhos spring water tunnel in porto city north west portugal it is possible that this study is the first record of moonmilk in an urban subsurface granitic environment the morphology and texture mineralogical composition stable isotope composition and microbial diversity of moonmilk deposits have been studied to infer the processes of moonmilk formation these whitish secondary mineral deposits are composed of very fine needle fibre calcite crystals with different morphologies and density calcified filaments of fungal hyphae or bacteria were distinguished by field emission scanning electron microscopy stable isotope analysis revealed a meteoric origin of the needle fibre calcite with an important contribution of atmospheric co2 soil respiration and hco3 from weathering of ca bearing minerals the dna based analyses revealed the presence of micro organisms related to urban contamination including actinobacteria mainly represented by pseudonocardia hispaniensis thaumarchaeota and ascomycota dominated by cladosporium this microbial composition is consistent with groundwater pollution and contamination sources of the overlying urban area including garages petrol stations and wastewater pipeline leakage showing that the paranhos tunnel is greatly perturbed by anthropogenic activities whether the identified micro organisms are involved in the formation of the needle fibre calcite or not is difficult to demonstrate but this study evidenced both abiotic and biogenic genesis for the calcite moonmilk in this subsurface granitic environment this article is protected by copyright all rights reserved

a holocene calcrete from north yorkshire england implications for interpreting palaeoclimates using calcretes glacial gravels of late devensian dimlington stadial age 26 000 13 000 years bp at west tanfield north yorkshire england have been cemented by carbonate rich solutions to produce a strongly indurated calcrete horizon the low mg cements occur as drusy spar needle fibres alveolar septal structures micrite and micropinnacles indicative of vadose zone cementation some complex pore partition structures attributed to precipitation along meniscus films also occur these partitions separate air dominated and water dominated microenvironments of the vadose zone the abundance of vadose fabrics shows that the accumulation is not a groundwater calcrete in addition much of the carbonate appears to have been precipitated by biological mediation carbon and oxygen isotopic data suggest that the carbonate did not form as a result of freezing as has been suggested for some arctic soil carbonates the pollen history of the area since the devensian suggests that this calcrete precipitated at low temperatures this contrasts with widely reported occurrences of calcrete in soils of hot arid or semi arid regions and suggests that palaeo calcretes should not be used as absolute palaeoclimatic indicators the unusual occurrence albeit localized of a thick calcrete under a cool and wet climate probably reflects the well drained nature of the gravels the abundance of caco3 as limestone clasts in the gravel and a high degree of biological activity beneath a forest cover which created a local environment favouring carbonate precipitation

different paleoenvironments of late pleistocene age identified in verőce outcrop hungary preliminary results abstract complex geomorphological geological paleopedological and chronometrical investigations were started to reveal the development of the alluvial section and the loess paleosol sequence containing remnants of a late palaeolithic site near ver ce hungary different paleoenvironments were identified in the profiles of the abandoned brickyard influenced by different facies in the margin of fluvial alluvial palaeo danube and proluvial southeast pediment of borzsony mountain area and the environments affected by the climate fluctuation of late pleistocene loess paleosol sequence overlying the base of alluvial materials sediments possibly deposited by palaeo danube were identified in a basal section of the abandoned brickyard the alluvial facies was indicated by sand silt and clay layers in the sediment sequence some parts of the alluvial sediments were covered by loess in the glacial periods intercalated by four paleosol horizons formed during interglacial or interstadial periods the sedimentation of loess and the forming of paleosols were finished by pedimentation processes sheet wash redeposition indicated by the fine layered material at the top of each paleosol horizon another complex fluvial alluvial section was identified at a different part of the brickyard possibly developed synchronous with the loess paleosol sequence during the late pleistocene based on relative and chronometrical dating methods e g archaeological stratigraphy and correlation of the artifacts 14c and luminescence dating the development of the loess paleosol sequence started in marine isotope stage 6 mis6 and the youngest layer dated to mis2

biogenic β fabric features in the hard laminated crusts of the mersin and adana regions southern turkey and the role of soil organisms in the formation of the calcrete profiles abstract this paper describes fabric features and their distribution in the calcretes and emphasizes the role of soil organisms in the formation of the calcrete profiles quaternary calcretes are common in the mersin and adana provinces occurring as powdery nodular tubular fracture infill and various forms of crusts the stable isotope values indicate calcrete development under semi arid climatic conditions and a pedogenic origin biogenic or fabric constituents are abundant in the hard laminated crust these are the rhizoliths alveolar septal structures needle fiber calcites calcified filaments spherical calcite bodies microcodium and vadose calcrete pisoliths rhizoliths have mainly formed by the petrification of roots and often contain cellular cortex structures the alveolar septal structure comprises root voids separated by a micritic wall or a bundle of tangentially oriented calcite needles needle fiber calcite is common in the hard laminated crust as monocrystalline rods and polycrystalline needles monocrystalline rods are smooth and small

metamorphism of the koraput alkaline complex eastern ghats province india evidence for reworking of a granulite terrane abstract an assemblage of predominantly metasedimentary rocks in the eastern ghats province india underwent granulite facies metamorphism and deformation in early neoproterozoic times and was subsequently intruded by the koraput alkaline complex the intrusion was earlier believed to be syn to late tectonic the gabbroic core of the complex hosts nepheline bearing syenitic dykes and veins following emplacement magmatic amphibole within the syenites and early orthopyroxene in feldspathic gneisses within the country rocks were retrogressed to biotite during pervasive solid state deformation subsequent prograde metamorphism resulted in the formation of anhydrous assemblages at the expense of relict magmatic amphibole within the syenites and metamorphic biotite in both the complex and the country rocks reactions reconstructed from textural observations indicate breakdown of biotite and amphibole to garnet clinopyroxene orthopyroxene bearing assemblages schreinemakers analysis on the relevant mineral associations suggests that heating was followed by loading of the region this indicates thermal rejuvenation of the complex and the host granulites during an intracrustal orogeny that post dates emplacement and cooling of the pluton available ages suggest that this event occurred in the mid neoproterozoic and is probably unrelated to the amalgamation of the granulite belt with the archaean bastar dharwar craton

co2 rich fluid inclusions in staurolite and associated minerals in a high pressure ultrahigh temperature granulite from the gondwana suture in southern india abstract we report the first detailed fluid inclusion study on mg al rocks from the gondwana suture zone along the palghat cauvery shear zone system in southern india these rocks underwent high pressure p 12 kbar and ultrahigh temperature t 990 c metamorphism during the late neoproterozoic associated with the collisional assembly of the gondwana supercontinent fluid inclusions of texturally primary and pseudosecondary categories occur in plagioclase staurolite and kyanite in these rocks inclusions of secondary nature are found in garnet and apatite all the trapped fluids show melting temperatures in the range of 58 6 to 56 6 c suggesting a dominantly pure co 2 composition the secondary inclusions show high homogenization temperatures t h of 12 9 to 30 0 c indicating low density of 0 59 0 83 g cm 3 although most of the primary and pseudosecondary inclusions also contain moderate to low density fluids 0 67 0 95 g cm 3 t h 3 5 to 27 4 c rare high density inclusions 1 00 1 06 g cm 3 t h 26 1 to 14 1 c were discovered in matrix plagioclase and porphyroblastic staurolite the estimated co 2 isochores for the high density primary and pseudosecondary inclusions intersect the clockwise p t trajectory of the rocks at around 8 3 9 0 kbar at 1000 c which broadly coincide with the peak metamorphic conditions of the area since these fluid inclusions show textural evidence for entrapment during the growth of the host high grade minerals we interpret the high density co 2 fluids to be traces of a co 2 rich synmetamorphic fluid that was present during the peak ultrahigh temperature metamorphism despite the preservation of high density co 2 inclusions in staurolite and plagioclase the primary and pseudosecondary inclusions in most of the other minerals show wide density variation which suggests the fluids in these inclusions underwent significant density reversal density decrease during decompression of the rocks from high pressure through the peak ultrahigh temperature stage along a clockwise p t trajectory the finding of pure co 2 inclusions in these mg al granulites conforms with similar observations from many other granulite facies terrains with the carbonic fluids probably derived from mantle reservoirs and transferred through deep seated shear zones that characterize this gondwana suture

reversed determination of the reaction phlogopite quartz enstatite potassium feldspar h 2 o in the ranges 750 875 degrees c and 2 12 kbar at low h 2 o activity with concentrated kcl solutions the reaction of phlogopite plus quartz to enstatite potassium feldspar and aqueous fluid in the system kmash kcl was reversed at 2 12 kbar and 750 875 degrees c and at low h 2 o activities by reversal of the h 2 o content of concentrated kcl solutions equilibrated with product and reactant assemblages synthetic 1m phlogopite kmg 3 alsi 3 o 10 oh 2 and enstatite mgsio 3 maintained end member stoichiometry throughout and the potassium feldspar kalsi 3 o 8 was a high sanidine based on unit cell refinements the broad p t xh 2 o and narrow reversal ranges of this investigation were possible because of the low and well defined h 2 o activity yet powerful fluxing action of concentrated kcl solutions solubility experiments on quartz and potassium feldspar in our p t xh 2 o range showed that fluid phase solution of silicate constituents was too small to have affected the h 2 o activity in the experiments the new determinations are more definitive than previous work done at very low pressures with pure h 2 o or in co 2 h 2 o mixtures they establish the standard free energy of the reaction in the experimental range with an uncertainty of about 1 kj and indicate that the synthetic phlogopite has maximal al si disorder under our experimental conditions the standard enthalpy of reaction at 298 k is 106 54 or 2 0 kj 2sigma based on our reversals a value 6 kj less positive than that currently used by many workers in calculations of biotite stability and h 2 o activity in the petrogenesis of high grade metamorphic rocks the lower thermal stability that we find for phlogopite requires revision in estimates of h 2 o activity of granulite facies metamorphism typical values for the natural assemblage orthopyroxene biotite garnet potassium feldspar plagioclase quartz at deep crustal metamorphic conditions 750 850 degrees c 5 10 kbar are alpha h2o 0 4 0 6 compared with values of 0 15 0 30 which would have been estimated with previously available data on phlogopite stability an important consequence of the expanded h 2 o activity range of granulites is that alkali chloride solutions of only moderate concentration xh 2 o 0 5 0 7 which are the values observed in actual fluid inclusions in many kinds of igneous and metamorphic rocks are a feasible alternative to the vapor absent conditions considered necessary by many workers based on previous low estimates of h 2 o participation of concentrated brines in deep crust upper mantle metamorphic processes enables alkali metasomatism and other kinds of chemical transport in an aqueous fluid without large scale melting of the crust

modulation of outer bank erosion by slump blocks disentangling the protective and destructive role of failed material on the three dimensional flow structure the three dimensional flow field near the banks of alluvial channels is the primary factor controlling rates of bank erosion although submerged slump blocks and associated large scale bank roughness elements have both previously been proposed to divert flow away from the bank direct observations of the interaction between eroded bank material and the 3 d flow field are lacking here we use observations from multibeam echo sounding terrestrial laser scanning and acoustic doppler current profiling to quantify for the first time the influence of submerged slump blocks on the near bank flow field in contrast to previous research emphasizing their influence on flow diversion away from the bank we show that slump blocks may also deflect flow onto the bank thereby increasing local shear stresses and rates of erosion we use our measurements to propose a conceptual model for how submerged slump blocks interact with the flow field to modulate bank erosion

fluid inclusion studies on the koraput alkaline complex eastern ghats province india implications for mid neoproterozoic granulite facies metamorphism and exhumation abstract following ultrahigh temperature granulite metamorphism at 1 ga the eastern ghats province of india was intruded by the koraput alkaline complex and was subsequently re metamorphosed in the granulite facies in the mid neoproterozoic time fluid inclusion studies were conducted on silica undersaturated alkali gabbro and syenites in the complex and a pre metamorphic pegmatitic granite dyke that intrudes it high density 1 02 1 05 g cc pseudo secondary pure co2 inclusions are restricted to metamorphic garnets within the gabbro and quartz within the granite whereas moderate 0 92 0 95 g cc and low density 0 75 g cc secondary inclusions occur in garnet magmatic clinopyroxene plagioclase hornblende and quartz the isochores calculated for high density pseudo secondary inclusions pass very close to the peak metamorphic window 8 kbar 750 c and are interpreted to represent the fluid present during peak metamorphism that was entrapped by the growing garnet microscopic round inclusions of undigested relict calcite in garnet suggest that the co2 present during metamorphism of the complex was internally derived through carbonate breakdown pure to low salinity 0 00 10 1 wt nacl equivalent aqueous intra intergranular inclusions showing unimodal normal distribution of final ice melting temperature tm and temperature of homogenization th are present only in quartz within the granite these represent re equilibrated inclusions within the quartz host that were entrapped at the metamorphic peak rare chemically precipitated graphite along the walls of carbonic inclusions is interpreted as a post entrapment reaction product formed during decompression the fluid inclusion evidence is consistent with rapid exhumation of a thickened lower crust following the mid neoproterozoic granulite facies metamorphic event the study suggests that mantle co2 transported by alkaline magma into the crust was locked up within carbonates and released during granulite metamorphism

co2 h2s cos s8 alo oh bearing fluid inclusions in ruby from marble hosted deposits in luc yen area north vietnam abstract fluid inclusions have been studied in rubies from marble hosted deposits in the luc yen mining district north vietnam raman and infrared spectroscopy combined with microthermometry investigations on primary and secondary fluid inclusions provided evidence of co 2 h 2 s cos s 8 alo oh bearing fluids with native sulphur and diaspore daughter minerals without visible water diaspore appeared as a nonvisible film of 2 3 m coating the wall of the fluid inclusion cavity and native sulphur was generally nucleated during raman irradiation the presence of diaspore and cos in the fluid inclusions indicates that water was present in the paleofluid the mole fractions of h 2 o and co 2 are around 10 2 and the expected concentration of water in the fluid inclusions is in the 1 10 mol range crush leach identified sulphates and chlorides that are assigned to the presence of anhydrite and na ca cl salts found by sem in the ruby crystals the co 2 rich inclusions which do not coexist with an aqueous phase by immiscibility process demonstrate that ruby grew from this co 2 rich and water poor fluid at equilibrium with na ca cl salts thermal reduction of evaporitic sulphates based on an initial assemblage of anhydrite calcite and graphite originating from the metamorphism of organic matter is proposed to explain the original fluid chemistry of these marble hosted rubies the marbles acted as a closed system and the carbonic composition of the parent fluids in ruby indicates that aluminium can be transported in co 2 rich fluids at high p t

a simplified 2d model for meander migration with physically based bank evolution abstract the rate of migration calculated by numerical models of river meandering is commonly based on a method that relates the rate of migration to near bank excess velocity multiplied by a dimensionless coefficient notwithstanding its simplicity since the early 1980s this method has provided important insight into the long term evolution of meander planforms through theoretical exercises its use in practice has not been as successful because the complexity of the physical processes responsible for bank retreat the heterogeneity in floodplain soils and the presence of vegetation make the calibration of the dimensionless coefficient rather challenging this paper presents a new approach that calculates rates of meander migration using physically based streambank erosion formulations the university of illinois rvr meander model which simulates meandering river flow and bed morphodynamics is integrated with algorithms for streambank erosion of the us department of agriculture channel evolution computer model concepts the performance of the proposed approach is compared to that of the more simple classic method through the application to several test cases for idealized and natural planform geometry the advantages and limitations of the approach are discussed focusing on simulated planform pattern the impact of soil spatial heterogeneity the relative importance of the different processes controlling bank erosion hydraulic erosion cantilever and planar failure the requirements for obtaining stable migration patterns centerline filtering and interpolation of bank physical properties and the capability of predicting the planform evolution of natural rivers over engineering time scales i e 50 to 100 years the applications show that the improved physically based method of bank retreat is required to capture the complex long term migration patterns of natural channels which cannot be merely predicted from hydrodynamics only

needle fiber calcite a critical review and a proposed classification abstract from a review of the recent literature and our own observations the different morphologies of needle fiber calcite are classified they can be characterized as monocrystalline rods with or without serrated edges or as polycrystalline chains the simplest monocrystalline habit of needle fiber calcite is the individual micro rod m larger monocrystalline rods ma exist in multiples of two more complex forms are found as paired monocrystalline rods with serrated plates along their length mb this group includes three habits which can be distinguished by the number of plates and their orientation relative to the rod finally there is a monocrystalline form mab intermediate between the categories ma and mb which shows the transition from the simple coupled rods to rods with errated plates although polycrystalline needles p have rarely been reported in the literature three types of morphologies have been identified each type of crystal has a specific origin the m micro rods are physicochemical nuclei or calcified bacteria they do not seem to evolve towards larger or more complex morphologies the ma rods are related to biomineralization inside the fungal sheaths the mb rods postdate liberation of ma rods from mycelian bundles the serrated plates are secondary syntactic crystallizations of physicochemical origin whose growth can be inhibited for various reasons the origin of p chains is less well understood but they seem to be physicochemical crystallizations related to evaporation and desiccation therefore these three groups m ma mb and p have similar morphologies but do not seem to be related genetically the only known link is between the ma and mb rods there is no evolutionary s quence of needle fiber calcite habits but a convergence of forms between crystals whose origins are different and independent structures described in the literature as convoluted random cutane and nest like are the result of either evolution of the mycelian bundles or movement of material and organisms in the soil in the case of m micro rods the microfabric is related to the random precipitation around nuclei in pores filled with a highly supersaturated solution initially the p chains also precipitate without preferential organization and later on the growth seems to preferentially constitute chains although the mechanisms are still not understood moreover needle fiber calcites do not indicate a particular climatic environment

calcite moonmilk crystal morphology and environment of formation in caves in the italian alps abstract calcite moonmilk which is a cave deposit formed of calcite crystals and water is found in many caves in the italian alps these modern and ancient deposits are formed of fiber calcite crystals 50 500 nm wide and 1 to 10 m long and polycrystalline chains that have few crystal defects radiocarbon dating indicates that most moonmilk deposits in these caves are fossil and that for most precipitation ceased 6400 cal years bp at the end of the mid holocene hypsithermal in the caves of the italian alps the optimal conditions for formation of calcite moonmilk are 1 a temperature range of 3 5 5 5 c 2 low discharge volumes of seepage waters that are slightly supersaturated sical 0 0 to 0 2 and 3 relative humidity that is at or close to 100 microbial activity apparently did not play an active role in the formation of the calcite moonmilk conditions for moonmilk formation are typically found in caves that are located beneath land surfaces which are soil covered and support a conifer forest precipitation of the fiber calcite crystals apparently involved very slow flow of slightly supersaturated fluids the fact that moonmilk appears to form under a narrow range of environmental conditions means that this cave deposit has potential as a paleoclimatic indicator in high alpine karst areas

geoarchaeological context of the later phases of mousterian occupation 80 115 ka at nesher ramla israel soil erosion deposition and pedogenic processes a new open air mousterian site was found in karst depression on hilly limestone terrain of central israel at nesher ramla the paper highlights the complex history of depositional post depositional and pedogenic processes that took place at the later phases of mousterian site formation during the osl age interval between 80 and 115 ka the upper sequence is divided into unit i and unit ii both comprising rather uniform calcareous gravel rich silty clay deposits gravel largely consists of calcrete nari and possibly some chalky limestone unit i is darker partially decarbonated magnetically enhanced and shows microscopic features of shrink swell process analogous to vertisols mousterian artifacts chunks of ochre and animal bones are scarce in this unit unit ii has increased gravel magnetic susceptibility values drop and humus and carbonate content both increase mousterian artifact density significantly increases in the middle part of unit ii lithologic characteristics thin sections and sem eds all indicate that the upper sequence originated from periodic erosion of loess derived soils developed upon chalky hillslopes intermittent with more stable periods when hominins occupied the site the proposed model relates the upper sequence to heterogeneous anthropogenic pedosediments with high proportions of eroded soil materials and signs of in situ pedogenesis apart from singular mm sized pyrogenic features remnants of bedded combustion features in the upper sequence are lacking probably because of pedogenic and diagenetic alterations on the site

a self limiting bank erosion mechanism inferring temporal variations in bank form and skin drag from high resolution topographic data fluvial bank erosion rates are often quantified by assuming that the erosion rate is a function of the excess above a critical threshold boundary shear stress applied by the flow research has shown that the form roughness induced by natural topographic bank features such as slumps spurs and embayments is the dominant component of the spatially averaged total shear stress meaning that form roughness provides an important control on bank erosion rates however measuring the relative components of the total shear stress for a natural system is not straightforward in this paper we employ the method of kean and smith 2006a b to partition the form and skin drag components of river bank roughness using a time series 2005 2011 of high resolution topographic surveys of an eroding bank of the cecina river in central italy this method approximates the form drag component of the roughness along a longitudinal bank profile as a series of user defined gaussian curves the extracted metrics are used in conjunction with an estimate of the outer region flow velocity to partition the form and skin drag components of the total boundary shear stress according to the kean and smith analytical solution the relative magnitude of the form and skin shear stress at each survey date is analysed alongside dems of difference to reveal that intense episodes of erosion are followed by periods of quiescence we show that this is due to the protection offered by increased form drag roughness following erosion we conceptualise the dynamic feedbacks that exist between river discharge bank erosion processes and bank form roughness into a simple model of the self limiting nature of river bank erosion

late quaternary paleoclimate in semiarid northeastern brazil from u series dating of travertine and water table speleothems abstract fossil travertine and subaqueous speleothems in presently dry caves suggest periods of enhanced ground water recharge during the quaternary period in semiarid northeastern brazil travertine deposits and water table speleothems were dated by the 230 th 234 u technique yielding new evidence for the timing of past periods of increased rainfall the travertine was deposited in two distinct phases extensive in situ deposits during marine isotope stage 2 and fragmentary indurated deposits dating to ca 400 000 yr b p possibly marine isotope stage 10 or 12 dating of water table speleothems showed that the regional water table was 13 1 m above the present level at the last glacial maximum a second site yielded ages suggesting a still higher water table during marine isotope stage 6 these new data demonstrate that northeastern brazil did not follow the general pattern of a dry last glacial maximum as suggested by other continental records in amazonia and southeastern brazil and as depicted in recent general circulation model gcm simulations our results thus indicate that significant variability in regional rainfall patterns occurred in the area during glaciations and caution against overgeneralization of paleoclimate patterns

pedogenic calcretes within fracture systems and beddings in neoproterozoic limestones of the irece basin northeastern brazil abstract calcretes or caliches are continental limestones developed by surficial weathering process that takes place mostly in arid and semi arid regions in the irece basin northeastern brazil in addition to the regular occurrence of pedogenic calcretes a peculiar type of structurally controlled calcretes occurs on neoproterozoic limestones these peculiar calcretes developed near the surface and occur 1 between layers 2 inside fractures and 3 within major thrust faults fieldwork on selected outcrops was integrated with petrographic mineralogic geochemical density and mercury intrusion porosity analyses to constrain the environment of formation and their petrophysical properties the results revealed that this type of calcrete is the product of multiepisodic events of dissolution and precipitation occurring during the wet and dry seasons in the region along fractures and beddings based on the petrophysical results we suggest that these calcretes may have an important role in the migration of fluids through the impermeable host carbonate rock and that they act as a conduit for fluid flow as revealed by their high porosity mean value 26 and remarkable pore connectivity

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

on the retreat of forested cohesive riverbanks abstract data from the brandywine creek in pennsylvania and the south river in virginia document spatial and temporal patterns describing the retreat of gently curving bends with forested riparian zones containing a mix of very large and smaller trees cohesive banks and slow rates of migration 0 1 m yr field data include 2 5 years of bank profile surveys measurements of tree morphology and ground based laser scanner lidar surveys repeated biannually these banks retreat through a cycle of erosion on decadal timescales initially small volumes mean 0 173 m3 per bank erosion event of soil are removed between large trees growing on the bank near trees the rate of bank retreat is initially negligible creating a scalloped bank morphology buttressed by large trees as the trees are increasingly exposed to the flow they become slowly undercut gradually leaning into the channel and sliding down to the toe of the bank eventually toppling into the river after a few years which restarts the cycle a magnitude frequency analysis of monitoring data from the brandywine creek indicates that the effective bank erosion event only 0 11 m3 thus forested bank retreat is dominated by small soil failures large erosion events many associated with trees toppling into the river greatly increase the variance of time averaged rates of bank erosion such that almost 4 years of monitoring are needed to measure time averaged rates of erosion to within an accuracy of 10 because of the limited spatial extent of our survey data and the absence of large discharges these results are provisional improved process based models to predict the retreat of forested riverbanks should account for the spatial structure of riparian forests and the interactions between the flow the gradual removal of bank soils and the ongoing efforts of the trees to remain attached to the bank

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

multi storey calcrete profiles developed during the initial stages of the configuration of the ebro basin s exorrheic fluvial network abstract multi storey calcrete profiles developed in the quaternary on strath terraces of the cinca and alcanadre rivers tributaries of the ebro river in ne spain two calcrete profiles tor 1 and tor 2 near the village of el tormillo show horizons with an arrangement that differs from that of commonly described calcrete profiles significant lateral changes occur in these profiles within a distance of less than 200 m reflecting their pedofacies relationship the tor 1 profile on terrace qt1 the highest and oldest consists of six horizons from bottom to top 1 coarse fluvial gravels 2 mudstones with carbonate nodules 3 a chalky horizon 4 laminar horizons including one peloidal horizon 5 a multi storey horizon formed of at least six minor sequences each of which includes a lower detrital layer a pisolithic horizon and a thin discontinuous laminar horizon these sequences indicate several cycles of brecciation and or reworking and 6 a topmost laminar and brecciated horizon also including reworked pisoliths some 200 m to the north of tor 1 horizon 5 undergoes a lateral change to channel fill deposits the infill of the channels shows a fining upwards sequence ranging from clasts of about 10 cm in diameter to red silts with sparse pebbles all the clasts come from the underlying calcrete horizons laminar horizons are interbedded with the clastic channel deposits the youngest calcrete profiles developed on terrace qt3 of the cinca river and on the qp4 and qp6 mantled pediment levels all show relatively simple profiles composed mostly of lower horizons of coated gravels with thin laminar horizons at the top most of the horizons especially the laminar ones show biogenic features such as alveolar septal structures calcified filaments biofilms spherulites micropores and needle like calcite crystals these features indicate the important role of vegetation in the formation of all the above profiles the interbedding of clastic sediments and pisolithic horizons within the tor 2 profile indicates several stages of stabilisation during profile formation these sequences are an indication of the sedimentation soil formation and reworking processes operating on the soil surface the alternation of these processes is interpreted as the result of climate vegetation changes the channel fills of tor 2 indicate erosion and reworking of the hard laminar calcrete horizon both tor 1 and tor 2 are multi storey profiles reflecting the complex sedimentation erosion pedogenesis relationships at the final stages of the development of its corresponding fluvial terrace the study of these calcretes shows that these supposedly abandoned terraces continue to be active even though the fluvial network is entrenched both the pedofacies relationships and the complexity shown by tor 1 and tor 2 reflect the complex and unstable geomorphic setting in which these profiles developed after the establishment of the exorrheic network less complex calcrete profiles were produced in the lower terraces

high density carbonic fluid inclusions in charnockites from eastern ghats india petrologic implications abstract charnockite rocks a significant litho unit in eastern ghats granulite belt eggb are characterized by the presence of dry mineral assemblage the anhydrous conditions required for the formation of ganulites are believed to be controlled by the lowering of water activity through the influx of co2 bearing fluids here we present the results of systematic petrographic and microthermometric studies characterizing the nature composition and density of co2 rich fluid inclusions in charnockitic rocks from gangarajumadugula in this study we have combined mineralogic thermobarometry with microthermometric data of the carbonic fluid inclusion population of high density in the charnockite samples from gangarajumadugula area to substantiate desiccation of lower crustal environment producing anhydrous conditions in the eastern ghats granulite belt close to peak pressure temperature calculations for core composition using convergence technique in present study indicate that these charnockites have experienced maximum p t around 860 c at 9 kbar which is broadly consistent with independent p t estimates inferred for gangarajumadugula area the reaction textures preserved by these charnockites and the thermobarometric data characterize decompression followed by cooling history high density carbonic fluid inclusions 1 08 g cm3 in quartz provide potential evidence for the involvement of co2 rich fluid during granulite facies metamorphism in eggb occurrence of co2 rich inclusions and elevated p t conditions open up the possibility favoring the mechanism of vapour deficient dehydration melting accompanied by co2 infiltration to account for charnockite formation from precursor crustal rocks our study documents that fluid inclusions in high grade metamorphic rocks have enormous potential in retaining worthwhile information of peak metamorphic conditions and understanding the metamorphic processes

fluid characteristics of high to ultrahigh temperature metamorphism in southern india a quantitative raman spectroscopic study abstract we report the first quantitative compositional data on fluid inclusions in late neoproterozoic to cambrian ultrahigh temperature uht granulites from major crustal blocks and shear zones in southern india fluid inclusions in various high grade minerals such as garnet orthopyroxene plagioclase cordierite and quartz from these rocks were studied in terms of petrography microthermometry and laser raman spectroscopy measured melting temperatures of the inclusions indicate that the trapped fluid phase is dominantly carbonic raman analyses confirmed a co2 rich composition with only minor dilutants such as n2 5 0 mol h2o 0 50 mol and ch4 0 47 mol the range of most co2 isochores computed from density measurements in fluid inclusions from the uht granulites pass below the peak pressure temperature conditions of metamorphism indicating considerable resetting of fluid densities during decompression in contrast garnetiferous granulites from the salem area along the palghat cauvery shear zone system which underwent high pressure prograde metamorphism contain very high density syn metamorphic pure co2 inclusions such dense carbonic fluid inclusions in garnet and plagioclase coexist with carbonate minerals calcite or dolomite indicating probable derivation from deep seated primary magmatic sources although models on the origin of co2 are debatable the ubiquitous association of carbonic fluids in the uht mineral assemblages is in favour of large scale infiltration of co2 rich fluids during extreme crustal metamorphism associated with collisional orogeny and subsequent extensional collapse at the final stage of amalgamation of the gondwana supercontinent

petrography micromorphology and genesis of holocene pedogenic calcrete in al jabal al akhdar sultanate of oman abstract holocene pedogenic calcrete nodules occur within quaternary terra rossa soil that fills shallow phytokarst cavities in the permian triassic carbonate sequence of al jabal al akhdar in the sultanate of oman they are preferentially clustered around plant roots and are almost wholly formed of calcite holocene pedogenic calcrete nodules developed within a mediterranean like climate that is characterized by intermittent wet and dry seasons petrographic examination revealed that the host terra rossa soil is partially calcitized and that the calcrete nodules consist of smaller coalesced diffused and or discrete granular nodules the latter consist of several types of rhizoliths floating in a groundmass formed of micrite and microspar as well as spar to a lesser extent several textures of calcrete groundmass are recognized the most common is partially neomorphosed micrite three types of rhizoliths are recognized root moulds root casts and petrified calcified root tissues the latter were developed by mimic replacement of the tissue cells by cytomorphic calcite sem investigation of the calcite forming the calcrete nodules revealed that it consists of closely stacked sheets formed of calcareous nanoglobules agglutinated by eps and entombed calcareous microbial fossils which indicate a biogenic origin the calcareous nature of the bedrock climatic conditions and prevalence of biological activities of microorganisms associated with the plant root system in the host soil have significantly controlled the development and texture of these nodules the relative abundance of scalenohedral calcite within the calcrete groundmass is attributed to the impact of mg ions and organic compounds it has been concluded that the studied pedogenic calcrete is a type of freshwater terrestrial thrombolitic microbialite this study may help improve the understanding of the palaeoenvironmental conditions of analogue fossil calcretes

the nagercoil charnockite a magnesian calcic to calc alkalic granitoid dehydrated during a granulite facies metamorphic event the paleoproterozoic nagercoil charnockite massif in southern india consists of garnet absent and garnet bearing varieties with garnet occurring only in those areas where the charnockite incorporates supracrustal lithologies there is a late neoproterozoic cambrian granulite facies metamorphic overprint on the charnockite massif this study examines whether orthopyroxene in the charnockites crystallized during the original magmatic stage or formed during the later high grade metamorphic event the textural association of orthopyroxene and relic garnet grains and reaction intergrowths of garnet and or biotite with orthopyroxene similar to those reported in dehydration zones within the gneisses surrounding the charnockite massif show that orthopyroxene in the charnockite massif formed during the late high grade metamorphic event from dehydration reactions and is not part of the original igneous assemblage metasomatic textures such as thin k feldspar rims together with the presence of co2 rich fluid inclusions in these rocks suggest that co2 metasomatism widely prevalent in the gneisses surrounding the massif probably resulted in the low water activity necessary to form orthopyroxene during the metamorphic overprint an oxygen isotope traverse along a metapelite enclave charnockite contact within the massif shows a distinct variation in d 18 o values with the charnockite away from the contact having the lowest d 18 o value 8 9o similar to that of typical metaluminous granitic rocks the charnockite at the contact shows an intermediate d 18 o value 10 3o and the surrounding metapelite has the highest d 18 o value 12o the intermediate d 18 o value indicates partial assimilation of metapelite with a high d 18 o value into the charnockite with a low d 18 o value both the garnet absent and garnet bearing charnockites have similar compositional ranges to tonalite granodiorite granite ttg suites irrespective of whether garnet is present or not the sr contents of the charnockites show a bimodal distribution a high sr group which is magnesian calcic to calc alkalic metaluminous showing ttg affinities and a low sr group which is dominantly ferroan calcic to calc alkalic metaluminous showing similarities to the orthopyroxene bearing dehydration zones petrogenetic characterization suggests that the protoliths of the nagercoil charnockites were high temperature melts of hydrous basalt

a new form of needle fiber calcite produced by physical weathering of shells needle fiber calcite is a common crystal form in soils and sediments from diverse environmental settings and it has been used as evidence of a specific soil development either past or present however it can have either a physicochemical or a biological origin and its ubiquity prevents straightforward use as an environmental proxy in this paper we present a new form of needle fiber calcite derived neither from biologically mediated mineralization in the soil nor from physicochemical precipitation this needle fiber calcite is monocrystalline and prismatic and is associated with the physical weathering of mytilus edulis linnaeus bivalve shells found in soils from anthropic shell middens located on the northern coast of the beagle channel argentina the effects of freeze thaw cycles can be observed in the local soils and would be responsible for the release of the calcite crystals that make up the outer layer of the shell in this respect the new form of needle fiber calcite would be specific for this process in anthropogenic soils in cold climates and could provide information on past climatic conditions

unravelling calcrete environmental controls in volcanic islands gran canaria island spain abstract volcanic islands are unique contexts to analyze the controls on calcrete development in settings with varied relief climate and vegetation and lacking carbonate host rocks this paper discusses the formation of quaternary calcrete profiles in gran canaria volcanic island under direct influence of the sal saharian air layer calcrete profiles are multi storey and composed of prismatic massive laminar pisolithic ooid bearing sandy mudstones with rhizoliths and brecciated horizons host rocks include basalts siliceous mudstones volcanic sands and gravels and bioclastic rich sands carbonate is mostly calcite but some dolomite occurs in massive horizons the main microfabrics include laminated micrite fine crystalline dolomite desiccated micrite micrite clay groundmass oriented mg rich clays peloids spherulites and coated grains 13c varies from 3 26 to 9 18 vpdb and 18o from 0 86 to 3 24 vpdb the 87sr 86sr ratios are between 0 707504 and 0 708860 indicating that calcium was mostly supplied from the caco3 rich aeolian dust coming from the sahara desert calcrete profiles are mostly pedogenic with roots and microorganisms enabling carbonate precipitation within the soils the correlation trend of 13c and 18o points to a climate control on precipitation with the heavier isotope values in the horizons containing dolomite sedimentation rates interplayed with calcrete formation processes and erosion to outline the profiles horizons amalgamated laminar horizons formed when the rate of calcrete formation was higher than sedimentation and erosion whereas areas or periods with relatively higher sedimentation allowed the separation of calcrete horizons the direction of the winds supplying aeolian dust and the varied relief vegetation and climate favored better development of calcretes in the relatively arid and lowland areas of the eastern side of the island our study shows that calcretes contain the record of the paleoenvironmental controls that operated in volcanic islands with no previous carbonate substrates

very high density co2 associated with ultrahigh temperature metamorphism in the eastern ghats granulite belt india spinel bearing high mg al granulites of the vizianagram area in the eastern ghats granulite belt show textural features clearly establishing that the association spinel ss quartz fe ti oxide solid solution sillimanite porphyroblastic orthopyroxene was stable during peak metamorphic conditions pressure temperature p t conditions estimated from both mineralogical thermobarometry and phase equilibrium limitations indicate that the peak metamorphism occurred under ultrahigh t conditions 1000 c at 8 9 kbar pressure retrograde p t conditions of 750 800 c 6 7 kbar are deduced from the compositions of coronal garnet and orthopyroxene which have rims of spinel against quartz indicating significant cooling with slight lowering of pressure quartz associated with the ultrahigh t assemblage at vizianagram contains ubiquitous single phase carbonic inclusions as isolated clusters that belong to two categories group i shows extremely high density homogenization temperature 51 1 8 c density 1 15 g cm 3 and group ii trapped relatively lower density fluids homogenization temperature 18 4 2 4 c density 1 05 g cm 3 the iso chores for group i inclusions pass through the peak metamorphic p t conditions whereas those for group ii coincide with the p t conditions of the formation of coronal garnet and orthopyroxene our study is the first report of very high density co 2 associated with the eastern ghats granulite belt rocks and provides a strong case for the presence of co 2 rich fluids during ultrahigh t metamorphism at lower crustal levels

bank and near bank processes in an incised channel abstract gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion the interaction of these forces control streambank mechanics hydraulic forces exerted by flowing water on in situ bank toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower bank profiles seepage forces exerted on in situ bank material by groundwater downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength data from a study site on goodwin creek ms usa clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore water pressures negative pore water pressures matric suction have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear a stable bank can be transformed into an unstable bank during periods of prolonged rainfall through 1 increase in soil bulk unit specific weight 2 decrease or complete loss of matric suction and therefore apparent cohesion 3 generation of positive pore water pressures and therefore reduction or loss of frictional strength 4 entrainment of in situ and failed material at the bank toe and 5 loss of confining pressure during recession of stormflow hydrographs relatively small frequent flows during the winter have the ability to erode failed bank materials maintain oversteepened unstable bank surfaces and promote prolonged periods of bank retreat channel migration and high yields of fine grained sediment confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe which steepens the bank for example more than 2 m of bank retreat occurred during the study period at the research site on goodwin creek northern mississippi the loss of matric suction negative pore pressures due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability apparent cohesion friction angle soil bulk unit weight and moisture content were measured in situ matric suction was measured continuously in situ with a series of five pressure transducer tensiometers a bank failure algorithm which combines the mohr coulomb approach for saturated conditions and the fredlund modification for unsaturated conditions was developed for layered cohesive streambanks the resulting equation has been used successfully to investigate the role of matric suction positive pore water pressures and confining pressure for layered streambanks composed of cohesive materials

the structure and diagenesis of rhizoliths from cayman brac british west indies abstract rhizoliths from the pleistocene ironshore formation are formed of a brown micrite core surrounded by sediment that is well cemented with 1 calcite rhomb chains 2 isolated calcite rhombs 3 calcified spherical bodies 4 types i and ii calcified epilithic and chasmolithic filaments and 5 grain coating calcite needle mats the friable host sediment has significantly less cement and lacks the grain coating calcite needle mats and type ii calcified filaments of the rhizoliths the sediment however contains calcite needles and a cryptocrystalline cement which do not occur in the rhizolith the contrast in the amount and type of cement between the rhizoliths and the encasing sediment points to the significant role that plants can play in carbonate diagenesis not only do the plant roots act as conduits for water of varying composition they also provide sites at which algae fungi and bacteria thrive these microorganisms serve to promote diagenesis in the rhizoliths the occurrence of the sediments in a coastal setting means that they are subjected to many different types of water ranging from freshwater to saltwater such variability along with the associated changes in the water chemistry may be responsible for the considerable variation in the cement associated with the rhizoliths

micromorphology and genesis of quaternary stromatolitic tufa crust within the exposed cretaceous rayda formation in al jabal al akhdar oman abstract this study aimed to improve the understanding of the causes of lamination in terrestrial tufa using samples of terrestrial quaternary stromatolitic tufa deposits occurring within narrow karst grooves carved along the bedding planes of the exposed cretaceous rayda formation in al jabal al akhdar oman these stromatolitic tufa deposits consist wholly of low mg calcite and are formed of vertically stacked laminated planar and digitate like columnar structures lamination is exhibited as vertically stacked couplets of dark micritic and light sparitic laminae significant variations in the abundance and thickness of the micritic laminae as well as progressive changes in the size and fabric of calcite in the sparitic laminae were recognised thorough microscopic and nanoscopic examinations revealed that these laminations initially developed as stacked indistinct micritic laminae formed of calcitic microbialite that had initially precipitated within a biologically active microbial biofilm which thrived on the wet bedrock surface this was followed by the growth of microglobules at certain horizons within the microbialitic laminae forming incipient discontinuous thin sparitic laminae consisting of laterally stacked biogenic skeletal disphenoidal calcite microcrystals the latter were further growing via abiogenic syntaxial precipitation of calcite forming coarsely crystalline dagger shape bladed calcite crystals these processes resulted in the formation of well developed lamination it is therefore suggested that the stromatolitic lamination has been generated through five consecutive stages of biogenic and abiogenic precipitation of calcite within initially developed microbial biofilms stable isotope values 13c and 18o suggest that these tufa deposits had precipitated from continuously renewed freshwater enriched with bicarbonate dissolved from the marine limestone bedrock during a cold pluvial period

numerical simulation of hydrodynamics and bank erosion in a river bend we present an integrated analysis of bank erosion in a high curvature bend of the gravel bed cecina river central italy our analysis combines a model of fluvial bank erosion with groundwater flow and bank stability analyses to account for the influence of hydraulic erosion on mass failure processes the key novel aspect being that the fluvial erosion model is parameterized using outputs from detailed hydrodynamic simulations the results identify two mechanisms that explain how most bank retreat usually occurs after rather than during flood peaks first in the high curvature bend investigated here the maximum flow velocity core migrates away from the outer bank as flow discharge increases reducing sidewall boundary shear stress and fluvial erosion at peak flow stages second bank failure episodes are triggered by combinations of pore water and hydrostatic confining pressures induced in the period between the drawdown and rising phases of multipeaked flow events

length scales and statistical characteristics of outer bank roughness for large elongate meander bends the influence of bank material properties floodplain vegetation and flow inundation this paper explores the length scales and statistical characteristics of form roughness along the outer banks of two elongate bends on a large meandering river through investigation of topographic variability of the bank face the analysis also examines how roughness varies over the vertical height of the banks and when the banks are exposed subaerially and inundated during flood stage detailed data on the topography of the outer banks were obtained subaerially using terrestrial lidar during low flow conditions and subaqueously using multibeam echo sounding mbes during near bankfull conditions the contributions of various length scales of topographic irregularity to roughness for subaerial conditions were evaluated for different elevation contours on the bank faces using hilbert huang transform hht spectral analysis statistical characteristics for discrete areas on the bank faces were determined by calculating the root mean square of normal distances from a tin surface results of the hht analysis show that the characteristics of roughness along bank faces composed primarily of non cohesive sediment and eroding into cropland vary with bank elevation and exhibit a dominant range of roughness length scales 15 50 m on the other hand bank faces composed predominantly of cohesive material and carved into a forested floodplain have relatively uniform topographic roughness characteristics over the vertical extent of the bank face and do not exhibit a dominant roughness length scale or range of length scales additionally comparison between local surface roughness for subaerial versus subaqueous conditions shows that roughness decreases considerably when the banks are submerged most likely because of the removal of vegetation and eradication of small scale erosional features in non cohesive bank materials by flow along the bank face thus roughness appears to be linked to the hydraulic conditions affecting the bank at least relative to conditions that develop when banks are exposed subaerially

numerical simulation of widening and bed deformation of straight sand bed rivers ii model evaluation in this paper the numerical model presented in the companion paper is tested and applied assessment of model accuracy was based on two approaches first predictions of evolution of a 13 5 km reach of the south fork of the forked deer river in west tennessee were compared to observations over a 24 yr period results suggest that although the model was able to qualitatively predict trends of widening and deepening quantitative predictions were not reliable simulated widths and depths were within 15 of the corresponding observed values but observed change in these parameters at the study sites were also close to these values simulated rates of depth adjustment were within 15 of observed rates but observed rates of channel widening at the study sites were approximately three times those simulated by the model in the second approach the model was used to generate relationships between stable channel width and bank full discharge the model was able to successfully replicate the form of empirically

hypogenic origin geologic controls and functional organization of a giant cave system in precambrian carbonates brazil abstract this study is focused on speleogenesis of the toca da boa vista tbv and toca da barriguda tbr the longest caves in south america occurring in the neoproterozoic salitre formation in the sao francisco craton ne brazil we employ a multidisciplinary approach integrating detailed speleomorphogenetic lithostratigraphic and geological structure studies in order to reveal the origin of the caves their functional organization and geologic controls on their development the caves developed in deep seated confined conditions by rising flow the overall fields of passages of tbv and tbr caves represent a speleogenetically exploited large ne sw trending fracture corridor associated with a major thrust this corridor vertically extends across the salitre formation allowing the rise of deep fluids in the overall ascending flow system the formation of the cave pattern was controlled by a system of sub parallel anticlines and troughs with nne ssw dominant orientation and by vertical and lateral heterogeneities in fracture distribution three cave stratigraphic stories reflect the actual hydrostratigraphy during the main phase of speleogenesis cavities at different stories are distinct in morphology and functioning the gross tree dimensional pattern of the system is effectively organized to conduct rising flow in deep seated confined conditions cavities in the lower story developed as recharge components to the system a laterally extensive conduit network in the middle story formed because the vertical flow from numerous recharge points has been redirected laterally along the highly conductive unit occurring below the major seal a scarcely fractured unit rift like and shaft like conduits in the upper story developed along fracture controlled outflow paths breaching the integrity of the major seal and served as outlets for the cave system the cave system represents a series of vertically organized functionally largely independent clusters of cavities developed within individual ascending flow cells lateral integration of clusters occurred due to hydrodynamic interaction between the flow cells in course of speleogenetic evolution and change of boundary conditions the main speleogenetic phase during which the gross cave pattern has been established and the caves acquired most of their volume was likely related to rise of deep fluids at about 520 ma or associated with rifting and the pangea break up in triassic cretaceous this study highlights the importance of speleogenetic studies for interpreting porosity and permeability features in carbonate reservoirs

carbonic metamorphism at ultrahigh temperatures evidence from north china craton abstract the north china craton ncc constitutes one of the fundamental precambrian nuclei of asia the paleoproterozoic khondalite belt along the northern margin of the ncc shows evidence for extreme crustal metamorphism at temperatures exceeding 1000 c and pressures of 10 12 kbar with the formation of diagnostic ultrahigh temperature uht mineral assemblages including sapphirine quartz high alumina orthopyroxene sillimanite and high temperature mesoperthites here we record for the first time the common occurrence of co2 rich fluid inclusions in peak uht minerals in the mg al granulites of ncc and trace the fluid evolution history from microthermometric and laser raman spectroscopic studies we show that the syn metamorphic fluid in the uht rocks was pure co2 while very high density carbonic fluids are preserved in some cases corresponding to entrapment at peak conditions many of the inclusions underwent density modification during the rapid and near isothermal exhumation of the rocks following peak uht metamorphism and initial cooling at depth the present study area within the northern margin of the ncc defines a collisional orogenic belt where continental collision and deep subduction were possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusions of paleoproterozoic age that are seen emplaced within the granulite facies supracrustals the thermal anomaly displayed by the uht granulites may thus correlate with asthenospheric upwelling and emplacement of mafic magmas possibly associated with plume activity which provided the heat and co2 input to achieve extreme crustal metamorphism and generation of dry granulite facies assemblages our study is the first report of syn metamorphic co2 rich fluids in uht granulites from a paleoproterozoic ca 1 92 ga terrane and provide evidence for carbonic metamorphism at ultrahigh temperatures as north china craton joined the columbia supercontinent amalgam

anticlockwise evolution of ultrahigh temperature granulites within continental collision zone in southern india abstract we report three new localities of corundum and sapphirine bearing hyper aluminous mg rich and silica poor ultrahigh temperature granulites formed during late neoproterozoic cambrian times within the palghat cauvery shear zone system in southern india from petrologic characteristics mineral chemistry and petrogenetic grid considerations the peak metamorphic conditions of these rocks are inferred to lie around 950 1000 c as suggested by al in orthopyroxene thermometer at pressures above 10 kbar as indicated by the equilibrium orthopyroxene sillimanite gedrite quartz assemblage these rocks preserve several remarkable reaction textures the most prominent among which is the triple corona of spinel sapphirine cordierite on corundum with the whole textural assembly embedded within the matrix of gedrite suggesting the reaction ged crn spl spr crd the formation of sapphirine sillimanite assemblage symplectite associated with relict corundum and porphyroblasitc cordierite is explained by the reaction crd crn spr sil the association of sapphirine cordierite symplectite with gedrite sillimanite assemblage as well as with aluminosilicate boundaries indicates the gedrite consuming reaction ged sil spr crd extensive growth of sapphirine cordierite observed on the rim of gedrite porphyroblasts with spinel occurring as relict inclusions within the sapphirine indicates the reaction ged spl spr crd the pressure temperature p t path defined from the observed mineral assemblages and reaction texture is characterized by anticlockwise trajectory with a prograde segment of initial heating and subsequent deep burial followed by retrograde near isothermal decompression such an anticlockwise trajectory is being reported for the first time from southern india and has important tectonic implications since these rocks were developed at the leading edge of the crustal block that was involved in collisional orogeny and subsequent extension during the final phase of assembly of the gondwana supercontinent we propose that the rocks were subjected to deep subduction and rapid exhumation and the extreme thermal conditions were attained either through input from underplated mantle derived magmas or convective thinning or detachment of the lithospheric thermal boundary layer during or after crustal thickening

fluid assisted granulite metamorphism a continental journey abstract lower crustal granulites which constitute the base of all continents belong to two series high pressure granulites generated by crustal thickening subduction and ultra high temperature granulites associated with crustal extension fluid inclusions and metasomatic features indicate that the latter were metamorphosed in the presence of low water activity fluids high density co2 and brines which have invaded the lower crust at peak metamorphic conditions fluid assisted granulite metamorphism high pressure and ultra high temperature granulites commonly occur along elongated paired belts they were formed from the early proterozoic onwards during a small number of active periods lasting a few hundreds of m y these periods were separated from each other by longer periods of stability each period ended with the formation of a supercontinent whose amalgamation coincided with low to medium pressure ultra high temperature granulite metamorphism immediately before continental break up it is proposed that large quantities of mantle derived co2 stored in the lower crust at the final stage of supercontinent amalgamation are released into the hydro and atmosphere during breakup of the supercontinent fluid assisted granulite metamorphism therefore appears to be an important mechanism for transferring deep mantle fluids towards the earth s surface possible consequences were for example the sudden end of proterozoic glaciations as well as the post cambrian explosion of life

characterization of oxide assemblages of a suite of granulites from eastern ghats belt india implication to the evolution of c o h f fluids during retrogression abstract we document complex intergrowth involving spinel ilmenite magnetite hematite corundum rutile in various combinations from a suite of granulite facies rocks of eastern ghats belt india individual oxide phase shows considerable compositional variation among textures and samples these textures arguably developed by oxidation reaction of early spinel and ilmenite solid solution from near peak to subsequent retrogressive stages oxygen fugacity is measured at a constant pressure of 8 kbar and different temperatures estimated from geothermometric analyses involving oxide and silicate bearing equilibria in different samples the calculated f o 2 values are 2 3 log units higher than the qfm buffer except for one sample uncertainties in f o 2 calculation in some samples arise presumably due to extensive compositional readjustment of different oxide systematics at lower temperatures the persistence of high f o 2 in mineral assemblages could be inherited from an oxidized precursor but field evidence and presence of h 2 o co 2 rich fluid inclusions in the studied samples imply possible involvement of externally derived oxidizing fluid in the later part of the retrograde history recent experimental and natural data suggest co 2 charged brine solution could be suitable for oxidation of mineral assemblages presence of brine inclusions are not detected but fluorine enriched nature of biotite grains could possibly provide some indication for its presence the mixed fluid possibly has its source in the crystallizing mafic magma emplaced at the lower crust that is exposed in the adjacent area

the biogenic origin of needle fibre calcite needle fibre calcite is one of the most ubiquitous habits of calcite in vadose environments caves deposits soil pores etc its origin either through inorganic indirect or direct biological processes has long been debated in this study investigations at 11 sites in europe africa and central america support arguments for its biogenic origin the wide range of needle morphologies is the result of a gradual evolution of the simplest type a rod this rod is the elementary brick which by aggregation and welding builds more complex needles the absence of cross welded needles implies that they are welded in a mould or under a longitudinal and unidirectional constraint before being released inside the soil pores the difference between the lengthening of the needles and the c axis can be explained by the existence of needles observed under a scanning electron microscope in organic sleeves which can act as a mould during rod growth complex morphologies with epitaxial outgrowths on straight rods cannot have grown entirely inside organic microtubes they must result from soil diagenesis after the release of straight rods in a soil free medium whisker crystals are interpreted as the result of growth and coalescence of euhedral crystals on a rod rhomb chains are considered to be the consequence of successive epitaxial growth steps on a needle during variations in growth conditions isotopic signatures for needle fibre calcite vary from 16 63 to 1 10 and from 8 63 to 2 25 for 13c and 18o respectively the absence of high 18o values for needle fibre calcite precludes a purely physicochemical origin evaporative for this particular habit of calcite as epitaxial growth cannot precipitate in the same conditions as initial needles needle fibre calcite stable isotopic signatures should be used with caution as a proxy for palaeoenvironmental reconstructions in addition it is suggested that the term needle fibre calcite should be kept for the original biogenic form the other habit should be referred to as epitaxial forms of needle fibre calcite

biologically induced accumulations of caco3 in orthox soils of biga ivory coast biologically induced accumulations of calcium carbonate have been found inside orthox soils under and around the native iroko tree milicia excelsa moraceae in biga ivory coast the nature of these accumulations and their origin were studied in two soil profiles directly under the tree and at a distance of 30 cm from the trunk microscale forms of caco3 include 1 wood pseudomorphic structures such as parenchyma cells cellulose fibers and calcitic vessel infillings 2 three types of rhombohedra and 3 needle fiber calcite nfc in addition large scale blocks exhibit three types of textures 1 micritic calcite which seems to be the original material 2 light colored sparite in moldic voids and 3 asymmetrical radiaxial laminated fibrous cement some micritic aggregates and hemi spherulites vaterite were found in the sap on the trunk as well as in soils on silica grains and the wood itself the mineralogy of all these carbonate forms is mainly a stoichiometric calcite or a moderately enriched mg calcite however some samples contain monohydrocalcite as well as two polymorphs of calcium oxalate weddellite and whewellite calcite precipitation is facilitated by the oxidation of oxalate by soil bacteria that contributes to the increase in ph in biga soils this is in contrast to conventional orthox soils therefore three conditions are necessary for biologically induced precipitation of calcium carbonate in orthox soils associated with iroko trees the presence of a large amount of oxalate originating from the tree and fungi the existence of an oxalotrophic flora for oxalate oxidation into carbonate and a dry season

fluid induced nucleation of y ree phosphate minerals within apatite nature and experiment part i chlorapatite this study investigates chlorapatite ideally ca10 po4 6cl2 from two spatially separated locations in the odegardens verk apatite mine bamble sector se norway which was partially metasomatized under amphibolite facies conditions relative to the original chlorapatite metasomatized areas in sample dl136 are enriched in oh and f depleted in na si and y ree and contain numerous inclusions 1 15 m of monazite and xenotime in contrast metasomatized areas in sample tn174 are enriched in f and si depleted in na show y ree abundances similar to the original chlorapatite and host only a few monazite and xenotime grains in order to define the role of fluids in the formation of y ree phosphate minerals associated with apatite a series of experiments covering wide ranges of temperature 900 300 c and pressure 1000 500 mpa for a series of fluid compositions pure h2o a 50 50 molar mix of h2o and caf2 and co2 with 1 2 wt h2o were conducted on unaltered chlorapatite from the odegardens verk in the h2o experiments features due to metasomatic alteration depletion in na si and y ree as well as numerous monazite and xenotime inclusions as observed in the natural sample dl136 were fully reproduced monazite and xenotime grains were also observed growing on the surface of the apatite in dissolution embayments in metasomatized areas in the 50 50 caf2 h2o experiments metasomatized regions are strongly enriched in f and si depleted in na show unchanged y ree abundances and contain only a very few small monazite and xenotime grains similar to what was observed in sample tn174 natural and experimental observation imply the presence of two coupled substitutions na y ree 3 2 ca2 and si4 y ree 3 p5 ca2 in the case of dl136 and h2o fluid experiments na and si4 went into solution whereas the released y ree contributed to the growth of monazite and xenotime within the metasomatized apatite structure for sample tn174 and the 50 50 caf2 h2o fluid experiments na in apatite became depleted but si was enriched thereby stabilizing the y ree in the now recrystallized fluor hydroxylapatite structure which retarded the growth of monazite or xenotime inclusions the basic conclusion of this study is that nucleation of monazite and xenotime in the metasomatized chlorapatite is principally a function of the composition of the infiltrating fluid and to a much lesser extent temperature and pressure