white mica crystallinity finite strain and cleavage development across a large variscan structure nw spain x ray diffraction analyses were performed on white micas formed under strain and low grade metamorphic conditions from sandstones and siltstones along a transect through the narcea antiform a large structure that separates the external from the internal zones of the variscan belt of nw spain the results indicate a close spatial relationship between the onset of metamorphism and the cleavage front at the cleavage front strain is characterized by oblate ellipsoids that have x y z ratios from 1 to 1 5 the x y z ratio increases westward up to 3 0 as does the grade of metamorphism and is accompanied by an increase in the 9crystallinity9 index of the white mica from very low to low metamorphic grade this increase corresponds qualitatively to an increase in penetrativeness of the axial planar cleavage in the western part of the narcea antiform the major deformation event was the development of kilometre scale reverse shear zones because of polyphase deformation these rocks are not suitable for quantitative strain analysis but qualitatively finite strain can be observed to be prolate and invariably larger in this region than in the eastern sector the metamorphic grade is higher in the western part of the narcea antiform with local maxima occurring next to the base of the shear zones the b 0 cell parameter a semi quantitative geobarometer measured in the white mica is chaotic in the eastern sector showing a clear detrital inheritance in the western sector it is rational due to complete re equilibration during thermal resetting the inverse correlation between finite strain and white mica 9crystallinity9 is close showing that the anchizone epizone limit can be related to the increase of finite strain above values of r s 1 5 the close relation between white mica 9crystallinity9 and strain is suitable for tracking strain variations in extensive fine grained siliciclastic rocks where no appropiate strain markers are found

thermal modeling of convergent and extensional tectonic settings for the development of low grade metamorphism in the welsh basin the lower paleozoic welsh basin of the u k caledonides shows a metamorphic transition from zeolite to low greenschist facies for which there are two radically opposing models of development the traditional model is of a syntectonic metamorphism associated with crustal thickening during basin inversion and cleavage development the alternative model links the metamorphism not to traditional ideas of crustal thickening but to thermal anomalies associated with the extensional development of a back arc basin these two models are tested by applying quantitative thermal modeling to crustal thickening and crustal extension tectonic settings specific to the welsh basin this basin has a unique and very well constrained record of its stratigraphic sedimentological and chronologic histories that is used here to provide the framework from which the dynamics of crustal evolution can be modeled crustal thickening models suggest that a higher pressure facies series with a pumpellyite actinolite to greenschist facies transition should be dominant in contrast extensional modeling suggests that a low pressure fades with a transition from prehnite pumpellyite to greenschist facies should be dominant the thermal evolution of the extensional setting is more compatible with the lower pressure metamorphic series that is recorded in metabasites as well as pelitic rocks of the region the metamorphic evolution is regarded as developing initially as a burial style which is then over printed by fabric development while at or near peak p t conditions thus giving an apparent syntectonic style of metamorphism

twenty years of groundwater evolution in the triassic sandstone aquifer of lorraine impacts on baseline water quality abstract the lorraine triassic sandstone aquifer ltsa which has already been the subject of a chemical and radioisotopic study 1979 is used to investigate the impacts of 20 a of large scale pumping on baseline water quality in parallel new sampling of the aquifer 2001 provides new inorganic geochemical data including trace elements that allow improving the knowledge of baseline conditions and hydrochemical functioning of a major sandstone aquifer the good correlation between 14 c activities temperature and depth along the main flow line indicate regular downgradient trends and possible water stratification unreactive tracers mainly stable isotope ratios 18 o and 2 h as well as c isotopes are used to define a timescale for the aquifer showing two groups of groundwater namely of modern and holocene age and late pleistocene age with a mixing zone baseline quality is then represented by a wide range of concentrations mainly the result of time dependent water rock interaction as already observed elsewhere in triassic sandstone aquifers some trace elements such as li rb cs which are not limited by solubility constraints show linear trends during saturated flow downgradient the chemistry is also specifically characterised by a regular increase in na and cl and locally so 4 as a result of evaporite dissolution related to overlying or basement limits the aquifer is mostly oxidising with a redox boundary marked by u decrease some 40 km from outcrop groundwater abstraction since the 1970s has created a strong lowering 10 150 m of the water table especially from 1970 to 1980 based on nine boreholes previously sampled in 1979 a decreasing evolution in radiocarbon content of the tdic together with significant evolution of 18 o content indicate that old groundwater has moved upgradient the major difference in terms of baseline evolution is observed using cl and na concentration and locally so 4 indicating an increasing influence of water circulation involving overlying or basement formations or of mixing with permian waters from the point of view of aquifer management the perceptible no 3 increase could provide information on the progress of any contamination under the aerobic conditions in addition the few key elements indicators of disequilibrium related to overlying or deep waters should be included in regular monitoring programmes

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

lithium in waters of a polar desert abstract lithium li concentrations were measured in a series of stream and lake samples from a cold dry desert the mcmurdo dry valleys mdv in southern victoria land antarctica li geochemistry has been of great interest and utility in part because of its solubility and mobility during rockwater interactions in general the values determined for the streams and the dilute lake waters in this polar desert environment are similar to those found in temperate streams and lakes the source of li to these waters is a combination of marine aerosol and crustal weathering within the stream channels the hypersaline hypolimnion of lake bonney has extremely high concentrations of li which has been concentrated via a previous drawdown of the lake and its subsequent evapoconcentration the different distributions of li within the lakes is also due to past climatic changes and their effects on the chemical evolution of the lakes the high relative mobility of li controls its distribution within the aquatic systems of this cold desert environment

the susceptibility of uk groundwaters to acidic deposition the weathering of minerals at shallow depths provides much of the sink for acidic atmospheric deposition the geology of the uk has been divided into four classes according to the extent to which the bedrock is likely to provide buffering and possibly give rise to acidic surface or groundwaters other modifying factors including soils superficial deposits and land use are also considered the likely sources and sinks of h in shallow groundwater systems are also reviewed most available groundwater data are derived from major aquifers often in carbonate bearing lithologies which afford excellent buffering and which are unlikely ever to be adversely affected by acidic deposition relatively few data exist for shallow groundwaters widely used for domestic supplies in rural areas especially in western and northern britain where groundwaters might be most affected acidic groundwaters and or surface waters are defined on the basis of their alkalinity and calcite saturation index si c acidic groundwaters are most likely to occur where 1 acid soils are found and glacial drift is thin or absent 2 the source of acidic inputs is high 3 carbonate minerals are absent 4 the residence time of water is short low alkalinity groundwater is found in many sandstone lithologies including the sherwood sandstone a major uk aquifer many lower palaeozoic strata and granites however existing data for susceptible areas are insufficient to show whether or not there have been significant long term changes in groundwater acidity or alkalinity

origin and significance of redistributional secondary porosity abstract redistributional secondary rds porosity is created by the dissolution of framework grains and cements and the simultaneous precipitation of reaction products in the nearby pore space aluminosilicate minerals and in particular feldspars are the usual precursors of rds porosity in sandstones common product minerals are authigenic quartz and clay minerals usually kaolinite this type of secondary porosity is almost ubiquitous in sandstones rds porosity has little effect on the total porosity of reservoir rocks and contrary to popular opinion cannot give rise to higher than expected porosities at depth petrographic criteria alone are an insufficient measure that the rock has undergone leaching resulting in porosity enhancement to demonstrate porosity enhancement due to leaching it is necessary to show that the porosity of the rock is statistically higher than would otherwise be the case for a rock of similar characteristics that has not been leached the dissolution precipitation reactions that give rise to rds arise from the inherent thermodynamic instability of minerals such as the feldspars and other aluminosilicates which formed under magmatic or metamorphic conditions when these minerals dissolve they add aluminium and silica to the pore fluid however the concentration of aluminium and silica in the pore fluid is buffered by clay minerals and quartz respectively during burial diagenesis thus any increase in the concentration of these components leads to the precipitation of an authigenic clay mineral and authigenic quartz carboxylic acids are claimed to have the capacity to complex aluminium and so increase the solubility of aluminium and eliminate the precipitation of a clay phase however they are unlikely to have any major effect on aluminium solubility in natural i e complex pore fluids in fact dissolution will occur in acid neutral or alkaline conditions at a rate that is kinetically controlled reaction rates speed up exponentially with increasing temperature and therefore depth resulting in the destruction of more and more unstable components this increase in the rate of destruction of unstable components at depth can give rise to what appears to be a late leaching event what is seen in fact is the natural culmination of the destruction of thermodynamically unstable phases at an ever increasing rate during burial thus for a rock of a given composition the fraction of the total porosity that is secondary will increase with burial depth until all labile components are consumed the behaviour of mineral mixtures in the presence of a moving pore fluid is an additional contributing factor to the ubiquity of rds porosity where two or more minerals add the same ion to the pore fluid then the steady state concentration of that ion which is reached at some distance down the flow path theoretically an infinite distance is a weighted average of the equilibrium solubilities of that ion with respect to the minerals that contribute the ion thus as the pore fluid approaches a steady state concentration of the ion it will be undersaturated with respect to the least stable minerals and oversaturated with respect to the most stable mineral hence rds porosity must form as a result of the dissolution of the least stable mineral and the precipitation of the most stable mineral although kaolinite is the most common dissolution product of feldspars with increasing temperature its stability field shrinks with respect to other clay minerals such as illite thus it is possible for feldspars and other aluminosilicates to decompose at depth to give illite and authigenic quartz the growth of fibrous illite together with the change from a dominantly primary to a dominantly secondary pore structure can give rise to a rapid loss of permeability with depth where changes in the clay mineral type do not occur the impact of rds porosity on the porosity permeability behaviour of sandstones is minimal up to secondary porosities of about 10 beyond this figure there is at present too little data to make a clear statement

recharge velocity and geochemical evolution for the permo triassic sherwood sandstone northern ireland the triassic sherwood sandstone group is a major european aquifer system it is also the principal groundwater source in northern ireland however key aspects of its regional hydrogeology such as age distribution and geochemical evolution remain largely unknown here the groundwater geochemistry and isotopic composition were investigated in order to evaluate groundwater recharge and flow processes in a complex regional hydrogeological setting the dominant geochemical processes such as dissolution of carbonate cements were determined from the major and trace element chemistry stable and radio isotope measurements were taken as residence time and flow path indicators and together with physical and geochemical groundwater modelling revealed groundwater ages of up to 9000 years the importance of infiltration from overland flow from springs deriving water from the adjacent cretaceous chalk aquifer and subsequently re infiltrating into the sherwood sandstone was confirmed in addition evidence was found of a slow recharge component through low conductivity mudstones that yielded significant groundwater resident times throughout the lagan valley these findings provide improved understanding of groundwater flow processes in northern ireland and serve as an example of methods that can be applied to water management elsewhere

the chemistry and origin of groundwater in triassic sandstone and quaternary deposits northwest england and some uk comparisons abstract the triassic sherwood sandstone group is a major uk aquifer in this study the groundwater geochemistry of a 60 km2 area has been investigated to improve the understanding of the hydrogeology of the area and to determine the origin of groundwater archived analyses of groundwater samples were interpreted to determine the dominant geochemical processes and subsequently samples were taken from selected sites for stable and radio isotope measurements near areas of direct recharge of the sherwood sandstone groundwaters are unsaturated with respect to carbonate minerals sulphate and chloride are contributed to the groundwater in the sherwood sandstone from the overlying quaternary glacial drift deposits and mercia mudstone the groundwater chemistry and isotopes of sulphate indicate that the source of sulphate is gypsum in the triassic sequence and the triassic derived glacial deposits a significant proportion of the calcium in groundwater is shown to be exchanged for sodium in the aquifer matrix however in the more mineralised waters carbonate minerals are precipitated because of contributions to the groundwater of calcium from dissolution of gypsum up piezometric gradient groundwaters are modem and have relatively high 14c and tritium contents the oldest water which was sampled for 14c is estimated to be about 4000 years older than the modern waters which were sampled from near recharge zones the groundwater regime in the study area may be compared and contrasted with triassic sandstone aquifers elsewhere in the uk incongruent carbonate dissolution occurs as described in the triassic of the east midlands the lower mersey basin and southwest england exchange reactions are important in determining the groundwater chemistry as found elsewhere in the triassic of northwest england and in contrast to the east midlands and southwest england

origin of the groundwater salinity and geochemical processes in detrital and carbonate aquifers case of chougafiya basin central tunisia summary comprehensive investigations of groundwaters were performed in the detrital and carbonate aquifers of the chougafiya basin central tunisia in the present review hydrochemistry and isotopic tools were combined to get an insight into the processes controlling mineralization recharge conditions flow pattern of groundwater and c chemistry in the investigated hydrological system analysis of the dissolved constituents revealed that several processes controlled the observed chemical composition i the dissolution of evaporitic minerals ii cation exchange reactions iii sulfate reduction under anaerobic conditions iv incongruent dissolution of carbonate minerals calcite dolomite coupled with gypsum dissolution and calcite precipitation and v silicates weathering data inferred from 18o and deuterium isotopes in groundwater samples indicated recharge with modern rainfall water characterized by lower 18o and 2h values is interpreted as recharged by non evaporated rainfall originating from mediterranean and atlantic air masses however water with relatively enriched 18o and 2h contents is thought to reflect the occurrence of an evaporation process related to the long term practice of flood irrigation the radiogenic 3h isotope data provided insight into the presence of two recharge periods in the investigated groundwaters waters with 3h contents of 1 tu clearly suggested the occurrence of a contemporaneous recharge probably during the last two decades carbon isotopes provided some insights into the timescales of groundwater flow but mainly revealed that main sources of c are active in the system these are likely dissolved biogenic co2 carbonate dissolution and incongruent reaction of the carbonate matrix mean residence times were determined after correction of the initial activities for dead c from the rock matrix and suggest ages ranging from the present day to the holocene in both upper cretaceous and mio pliocene groundwaters

the spatial variation of weathering and soil depth across a triassic sandstone outcrop in this study we used an archive of borehole logs from the british geological survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the triassic sherwood sandstone group outcrop 750 km2 in the east midlands uk the borehole logs were used to estimate the thickness of the soil n 280 and soil and saprolite ss the overburden of ice may have increased sub glacial pore water pressure with the fractures and faults acting as a drainage system for the removal of dissolved weathering products

the dynamics and origin of groundwater salinity in the northeast hufu plain the aim of this research is to identify the dynamic characteristics and origins of groundwater salinity in the hufu plain samples of groundwater were taken from wells throughout the hufu plain geochemical analyses using integrated ionic ratios with a variety of graphical approaches saturation indices and the gis method were performed to distinguish the sources of groundwater salinity the results indicated that the groundwater can be classified into five main types the cation and anion trends were ca2 na mg2 k and hco3 so42 cl no3 respectively groundwater quality in the hufu plain is influenced by the chemical weathering of rock forming minerals the variation in saturation indices for different minerals indicated that groundwater salinization was controlled to some degree by human activities in the hufu plain groundwater salinity is not only governed by mineral weathering and dissolution such as calcite aragonite dolomite and gypsum but also significantly influenced by anthropogenic inputs such as fertilizer pesticide and sewage irrigation groundwater salinity originates mainly from the dissolving of gypsum and anhydrite and from anthropogenic inputs rather than from the weathering precipitation and dissolution of calcite dolomite and aragonite

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

relationships between very low grade metamorphism and tectonic deformation examples from the southern central iberian zone iberian massif variscan belt abstract we have studied the syn kinematic very low grade metamorphism in a polyphase variscan deformed region using x ray diffraction techniques two phases of regional metamorphism are related to their respective episodes of penetrative deformation in the southern central iberian zone the data obtained suggest that the rocks did not reach metamorphic equilibrium but strain favoured the progress of mineral reactions in the more deformed parts the first deformation is devonian in age and consists in a heterogeneous ductile shearing coeval with large scale recumbent folding that were produced under high anchizone to epizone metamorphic conditions the heterogeneity of the shearing originated strain gradients that can be said to enhance the growth of new minerals and the illite polytype transformation in the highly strained overturned limb of the preserved pile of recumbent folds but illite crystallinity remained constant throughout the structure the second deformation is mid carboniferous in age and consists in an upright folding that took place under late diagenesis to low anchizone metamorphic conditions the distribution of mineral parageneses and illite crystallinity across one of the upright folds suggests that strain gradients favoured the metamorphic reaction progress from the hinge low strain towards the limbs high strain other characteristics of the region such as a metamorphic gap associated with an unconformity at the base of the lower carboniferous rocks or cryptic contacts aureoles surrounding volcanic intercalations and a large granitic batholith are also studied

regional variations in water quality and relationships to soil and bedrock weathering in the southern sacramento valley california usa abstract regional patterns in ground and surface water chemistry of the southern sacramento valley in california were evaluated using publicly available geochemical data from the us geological survey s national water information system nwis within the boundaries of the study area more than 2300 ground water analyses and more than 20 000 surface water analyses were available ground waters from the west side of the sacramento valley contain greater concentrations of na ca mg b cl and so 4 while the east side ground waters contain greater concentrations of silica and k these differences result from variations in surface water chemistry as well as from chemical reactions between water and aquifer materials sediments that fill the sacramento valley were derived from highlands to the west the coast ranges and east the sierra nevada mountains the former having an oceanic provenance and the latter continental these geologic differences are at least in part responsible for the observed patterns in ground water chemistry thermal springs that are common along the west side of the sacramento valley appear to have an effect on surface water chemistry which in turn may affect the ground water chemistry

identification of spatio seasonal hydrogeochemical characteristics of the unconfined groundwater in the red river delta vietnam abstract groundwater has been the primary source of daily water supplies for people living in the red river delta the second largest delta in vietnam for this reason identification of hydrogeochemical properties of the groundwater is indispensable for sustainable utilization of groundwater sources in this study the spatio seasonal hydrogeochemical characteristics of groundwater in the unconfined aquifer of the red river delta have been investigated by systematically applying self organizing maps som and gibbs diagrams the groundwater chemistry dataset used in the analysis is composed of eight major dissolved ions i e ca2 mg2 na k hco 3 cl so 4 2 and co 3 2 and total dissolved solids that are collected from 47 groundwater monitoring wells within the study area during the dry and rainy seasons the som application classified the hydrogeochemical data into five clusters which revealed three basic representative water types high salinity one cluster low salinity two clusters and freshwater two clusters the spatial distribution of clusters and water types were identified in particular the low salinity type was found not only in the downstream area but also in the northeastern parts of the upstream and middle stream areas where the groundwater was mainly classified into one specific cluster in which agricultural activities were considered to influence groundwater chemistry cluster changes from the dry to rainy seasons were detected in approximately one fifth of the observations wells dilution by surface water may significantly affect the chemical characteristics of the unconfined aquifer during the rainy season based on gibbs diagrams rock weathering was found to be the main process in the evolution of chemical composition of freshwater type whereas the chemical structure of the low and high salinity types was primarily controlled by saltwater intrusion or anthropogenic activities

vertical groundwater flow in permo triassic sediments underlying two cities in the trent river basin uk the vertical component of groundwater flow that is responsible for advective penetration of contaminants in sandstone aquifers is poorly understood this lack of knowledge is of particular concern in urban areas where abstraction disrupts natural groundwater flow regimes and there exists an increased density of contaminant sources vertical hydraulic gradients that control vertical groundwater flow were investigated using bundled multilevel piezometers and a double packer assembly in dedicated boreholes constructed to depths of between 50 and 92 m below ground level in permo triassic sediments underlying two cities within the trent river basin of central england birmingham nottingham the hydrostratigraphy of the permotriassic sediments indicated by geophysical logging and hydraulic packer testing demonstrates considerable control over observed vertical hydraulic gradients and hence vertical groundwater flow the direction and magnitude of vertical hydraulic gradients recorded in multilevel piezometers and packers are broadly complementary and range within error from 0 1 to 2 0 7 groundwater is generally found to flow vertically toward transmissive zones within the hydrostratigraphical profile though urban abstraction from the sherwood sandstone aquifer also influences observed vertical hydraulic gradients bulk downward darcy velocities at two locations affected by abstraction are estimated to be in the order of several metres per year consistency in the distribution of hydraulic head with depth in permo triassic sediments is observed over a one year period and adds support the deduction of hydrostratigraphic control over vertical groundwater flow q 2003 elsevier b v all rights reserved

sub greenschist facies metamorphism from the variscides of sw ireland an early syn extensional peak thermal event illite crystallinity studies on metaclastics from the variscides of sw ireland range in value from 0 18 to 0 25 2 indicating a metamorphic grade in the upper anchizone lower epizone c 275 325 c chlorite geothermometry yields a similar metamorphic temperature range 280 315 c combining these data with known overburden estimates for the area c 5km implies late palaeozoic geothermal gradients in excess of 60 ckm 1 fluid inclusion studies on quartz veins in these metaclastics reveal two vein types characterized by fluid densities of 0 7 0 93 g cm 3 group 1 and 0 9 1 0gcm 3 group 2 respectively this variation in fluid density is thought to be dominantly controlled by temperature with group 1 veins linked to late palaeozoic extension and high geothermal gradients and group 2 veins associated with subsequent variscan deformation and lower temperature conditions

mass movements related to tectonics in the aspromonte massif southern italy abstract geomorphic and structural studies have been carried out on the headwaters of vallone colella torrent in an area intensely affected by mass movement phenomena on the aspromonte massif of southern italy rock types outcropping in the area are mostly gneiss and granitoids with subordinate presence of metarenites phyllites and biotite schists all lithologies experienced low grade metamorphism as indicated by petrographic analysis structural surveys performed at macroscopic and mesoscopic scale allowed recognition of several sets of discontinuities related to different deformation events the upper reaches of vallone colella torrent present a large active landslide zone the debris materials of which feed the debris flows along the drainage system towards the main valley mass movement phenomena are both shallow and deep seated the latter are limited to a sector of the study area while shallow processes are present throughout the landslide zone some considerations of the relationship between tectonics and mass movement are presented with particular reference to the presence of a large scale downthrown wedge bounded by structural surfaces on both sides of the valley located in the same area affected by deep seated phenomena

the nitrogen isotope composition of groundwater nitrates from the east midlands triassic sandstone aquifer england abstract the 15 n 14 n composition of nitrates dissolved in groundwaters from 23 abstraction sites in the east midlands sherwood sandstone are reported dissolved n 2 ar ratios are with two exceptions consistent with atmospheric input and show that denitrification does not occur throughout most of the aquifer the nitrogen isotope composition of nitrates dissolved in the groundwaters can be shown not to have been mixed or fractionated to any significant extent within the aquifer the observed 15n no3 isotopic variations are attributed to four nitrate sources all of which are associated with agricultural land use

zebra dolomitization as a result of focused fluid flow in the rocky mountains fold and thrust belt canada discordant zebra dolomite bodies occur locally in the middle cambrian cathedral and eldon formations of the main ranges of the canadian rocky mountains fold and thrust belt they are characterized by alternating dark grey a and white b bands forming an abba diagenetic cyclicity these bands developed parallel to both bedding and cleavage dark grey a bands consist of fine 300 m non planar crystalline impure dolomite the white b bands are composed of coarse up to several millimetres milky white pure saddle dolomites b1 which are often covered by pore lining zoned dolomite b2 the b phases often possess a saddle shaped morphology in contrast to the replacement origin of the a dolomite the zoned b2 dolomite rims are interpreted as a cement formed in open cavities the b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non carbonate components all the zebra dolomites studied are nearly stoichiometric and are characterized by enriched na and depleted sr concentrations fe and mn concentrations in these dolomites differ depending on the sample locality fluid inclusion data indicate that the dolomites formed from relatively hot th 130 200 c saline 20 23 wt cacl2 eq fluids a diagenetic high temperature origin is also supported by depleted 18o values 20 to 14 vpdb a contribution of 87sr enriched fluids is reflected in the 87sr 86sr values 0 7091 0 7123 zebra dolomite development is explained by focused fluid flow which exploited areas of structural weaknesses e g basin platform rim areas faults etc expulsion of hot basinal brines in a tectonically active regime generated overpressures which explains the development of secondary porosity during zebra dolomitization as well as the intra zebra fracturing at decimetre to micrometre scale

kinematic evolution of fault ramps and its role in development of landslides and lakes in the northwestern argentine andes the quebrada del toro and quebrada de las conchas in the cordillera oriental of northwestern argentina are notable for repeated landsliding and damming of major drainages both areas correspond to displacement transfer zones along major thrust systems that developed during the neogene uplift of the central andes during this period displacement transfer zones were areas of subdued relief that localized where rivers cross the fault systems however neotectonic deformation converted the transfer zones into restraining bends along strike slip systems resulting in enhanced uplift at river crossings the antecedent streams responded by rapidly downcutting into the ascending hanging wall blocks producing precipitous local relief the extreme local relief that was controlled by the kinematic evolution of faulting in both areas provides an effective precondition for landsliding which may have been ultimately triggered by seismicity and gravitational failure aided by enhanced undercutting during past humid conditions

distribution of landslides adjacent to the northern side of the yarlu tsangpo grand canyon in tibet china this paper presents results of recent studies on distribution and category of landslides in one section of the sichuan tibet highway adjacent to the northern side of the yarlu tsangpo grand canyon tibet southwestern china in the tectonic setting predominated by compression and strike slipping active faults are dominant and result in the genesis of the great alpine relief together with fluvial incision and unloading in this section with a distance of about 290 km between ranwu and lulang 34 landslides occurred among them the 12 large and super large landslides comprise the most dangerous part of the highway system to road users over the past 50 years the landslides usually occurred in slopes comprised of moraine with a large thickness fluvio pluvial and lacustrine deposits and fractured rocks based on the examination of the physical geography structural geology quaternary geology stratigraphy and petrography this paper presents the temporal spatial distribution of landslides along the section and classification of them into three types with respect to mechanism and composites of landslides type 1 landslide initiated at high elevation and transformed into a distal debris flow damming the river with a long reoccurrence interval type 2 landslide at stream banks in different ranks of mass movements in dissecting layers of moraines type 3 landslide of fractured rock mass with quick translation movements each of the three types is presented by distinctive case examples type 1 is yigong landslide type 2 includes dongjiu landslide group 102 landslide group suotong landslide group songzong landslide and the type 3 is layue landslide a binary landslide which is seldom seen in nature and which occurred in the outlet of one creek under the integrative function of fluvial incision and road cut is also presented these are distributed in different parts of the area with characterized structural geology topography and composites gneiss and quaternary deposits with accumulative quantity between suotong and dongjiu the most occurred with frequent and rapid translation shallow shearing planes various influential factors and unique triggering factors and a variable period of reoccurrence with a tendency of increasing magnitude in this region six influential factors greatly contribute to their occurrence a intensive neotectonic movements b ongoing alpine canyon relief c earthquakes d heavy precipitation e stream erosion and f human activities to a certain extent mostly the latter four factors play major roles in triggering landslide occurrence the earthquake causes the rock and soil to fracture and deform and tends to be unstable or cause earth induced landslides the heavy rainfall in monsoon seasons which saturates the soil and lower the shearing strength is mostly responsible for the occurrence of landslides the stream erosion disturbs slope toes causing progressive failure road construction and deforestation decrease the natural slope stability comments and suggestions on the physical measures for remediation of landslides and safety of highways are also made

interaction between shallow and deep aquifers in the tivoli plain central italy enhanced by groundwater extraction a multi isotope approach and geochemical modeling abstract in the tivoli plain rome central italy the interaction between shallow and deep groundwater flow systems enhanced by groundwater extraction has been investigated using isotopic and chemical tracers a conceptual model of the groundwater flowpaths has been developed and verified by geochemical modeling a combined hydrogeochemical and isotopic investigation using ion relationships such as dic cl ca ca mg so 4 so 4 hco 3 and environmental isotopes 18 o 2 h 87 sr 86 sr 34 s and 13 c was carried out in order to determine the sources of recharge of the aquifer the origin of solutes and the mixing processes in groundwater of tivoli plain multivariate statistical methods such as principal component analysis and cluster analyses have confirmed the existence of different geochemical facies and the role of mixing in the chemical composition of the groundwater results indicate that the hydrochemistry of groundwater is characterized by mixing between end members coming directly from carbonate recharge areas and to groundwater circulating in a deeply buried meso cenozoic carbonate sequence the travertine aquifer is fed by both flow systems but a local contribution by direct input in the plain has also been recognized the stable isotope data 18 o 2 h 13 c and 34 s supports the flow system conceptual model inferred from the geochemical data and represents key data to quantify the geochemical mixing in the different groundwaters of the plain the results of numerical modeling phreeqc are consistent with the flowpaths derived from the hydrogeochemical conceptual model the inverse models performed generated the main geochemical processes occurring in the groundwater flow system which also included mixing geochemical and isotope modeling demonstrate an increasing influence of groundwater from the deeply buried aquifer in the travertine aquifer enhanced by lowering of the travertine aquifer water table due to quarry pumping

isotope and minor element geochemistry of high arsenic groundwater from hangjinhouqi the hetao plain inner mongolia abstract high as groundwater is widely distributed in the northwestern hetao plain an arid region with slow groundwater flow arsenic concentration in groundwater ranges from 1 to 1000 g l most water samples have elevated salinities with cl and or hco 3 as the dominant anions and na as the dominant cation high concentrations of as in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic c doc nh 4 dissolved sulfide arsenite and dissolved ch 4 and relatively low concentrations of no 3 and so 4 2 results of the hydrochemical and h and o isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b f and br in groundwater in na hco 3 dominated groundwaters as b and f were enriched decades of irrigation using yellow river water has resulted in elevation of the groundwater level which has accelerated salt accumulation in shallow groundwater and surface soil in addition irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters as indicated by minor element and isotope geochemical data used to trace groundwater flow paths sr isotope composition also indicates that bedrock weathering is one of the primary sources of as in groundwater in the study area

hydrochemical evidence of the depth of penetration of anthropogenic recharge in sandstone aquifers underlying two mature cities in the uk pollution of urban groundwater is routinely reported but the profile of contamination with depth in urban aquifers is rarely resolved this limits understanding of the depth of penetration of urban recharge and contaminants and use of urban groundwater penetration of anthropogenic solutes major ions trace metals in permo triassic sandstone aquifers underlying two mature conurbations in the uk was investigated through depth specific groundwater sampling of dedicated multilevel piezometers identification of solute origin and biogeochemical processes e g denitrification mineral dissolution was aided by use of stable isotope ratios 34 s 32 s 18 o 16 o 15 n 14 n 13 c 12 c and chemical speciation modelling phreeqc depth profiles of aquifer hydrochemistry reveal penetration of anthropogenic solutes to depths of between 30 and 47 m below ground in the unconfined sandstone and confirm the contributions of faecal and industrial effluents to urban recharge they also highlight the complexity of solute loading and difficulty resolving solute origin from the range of potential sources in urban groundwater faecally derived no3 is the most pervasive contaminant exceeding drinkingwater quality guidelines and is associated with elevated concentrations of b and so4 elevated concentrations of li b cr and co are observed at depth in groundwater contaminated by long term industrial land use metalworking observed penetration of anthropogenic solutes in the unconfined sandstone is consistent with post development recharge of urban groundwater residence times 230 a indicated by flow modelling and suggests tentatively that urban abstraction to depths of up to 50 m below ground in the unconfined permo triassic sandstone is required to scavenge contaminated groundwater

geochemical controls on arsenic and rare earth elements approximately along a groundwater flow path in the shallow aquifer of the hetao basin inner mongolia article i nfo groundwaters and sediments were sampled approximately along a groundwater flow path in the shallow aquifer of the hetao basin inner mongolia along a flow path with a length of about 9 km groundwater evolves from ca hco3 so4 through mg ca hco3 cl to na cl hco3 from the recharge zone to the discharge

modelling the effect of forest cover in mitigating nitrate contamination of groundwater a case study of the sherwood sandstone aquifer in the east midlands uk summary as the second largest aquifer in the united kingdom the sherwood sandstone is threatened by high nitrate concentrations and water shortages land use change from arable agriculture to woodland could help mitigate agricultural diffuse pollution and this study provides an evaluation of the effects of woodland cover on groundwater quality six land use change scenarios focusing on two public supply borehole capture zones on the unconfined sherwood sandstone aquifer in nottinghamshire were examined in predictive simulations of nitrate concentrations until 2025 groundwater flow modelling modflow and mass transport modelling mt3dms incorporating outputs from a groundwater recharge model and an export coefficient model enabled a quantitative comparison between different scenarios on groundwater quality results revealed that the greatest decrease by 2025 in nitrate concentration 35 was associated with the entire target zone covered with forest whereas a decrease dependent on the application of best agricultural practice achieved a 20 reduction conversion of 80 ha and 240 ha of agricultural land to woodland in two borehole capture zones with areas of 210 ha and 484 ha respectively could potentially restrict nitrogen losses such that the eu groundwater nitrate limit 50 mg l 1 could be achieved in abstracted groundwater it is concluded that the combination of forest creation and application of best agricultural practice in a borehole capture zone is a recommended approach to control nitrate pollution in the long term and provides scientific support for pollution control strategies that rely on land use change to woodland to achieve water quality objectives

modelling the impact of forest cover on groundwater resources a case study of the sherwood sandstone aquifer in the east midlands uk land use change from arable agriculture to forestry has become a focus in many european countries to control leaching of non point agricultural pollutants such as nitrate to aquifers however a reduction in groundwater recharge beneath forest areas could potentially exacerbate water supply shortages no direct study has previously been undertaken in the uk to assess the effect of increasing woodland cover on the quantity of groundwater resources to address this knowledge gap this study applied a groundwater flow model modflow with a soil moisture balance recharge model to predict the effect of land use change to forestry on groundwater recharge and levels by 2025 at two public supply borehole sites on the unconfined sherwood sandstone aquifer in nottinghamshire four land use change scenarios focusing on borehole capture zones were developed the recharge calculations revealed a reduction of up to 45 in annual recharge as a result of an increase in woodland cover in the borehole capture zones with the reduction more marked in winter than in summer at both borehole locations however the associated decrease in groundwater levels was limited owing to the high storage capacity of the sandstone aquifer even with an increase in woodland cover over the entire target zone the simulated decrease in groundwater levels was less than 0 3 m it is concluded that a quantitative analysis using a modelling approach can assist in the better targeting of pollution control strategies that include land use change to woodland helping decision makers balance the expected improvements to groundwater quality while concurrently managing groundwater resources

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

the 102 landslide human slope interaction in se tibet over a 20 year period the evolution of large scale landslides should be studied because over long periods of time primary remediation measures may suffer reduced efficiency or have to be adjusted many times the 102 landslide in southeast tibet which originally formed in 1991 with a volume of 5 1 million m3 and still exhibits post failure activity provides a distinctive case study the landslide evolved from earthquake destruction and unloading rainfall triggered sliding and debris flow to sands sliding slopes the ne ringed scarp receded by 38 96 m during a five year period 2003 2008 the total recession was 160 m with a total area of 2500 m2 during a 17 year period 1991 2008 although several types of remediation measures were applied and were temporarily effective the normal function of the sichuan tibet highway was affected by landslide reactivation from time to time actual effects of the engineering measures such as retaining walls prestressed anchor cables and drainage ditches confirm that hasty governance of this type of large scale landslide is generally unfeasible over long time periods finally an approach involving a tunnel running backward from the front face has been adopted as a permanent solution to large scale moraine slope failures this engineering practice has been in progress since april 2012 this paper describes the evolution of the 102 landslide the engineering interventions to mitigate the effects of the landslide on the sichuan tibet highway and the choice of tunneling as a final mitigation measure the present study concludes that approaches that allow escape from developing geo hazards should always be the initial choice

hydrogeochemical and isotopic constraints on the origins of dryland salinity murray basin victoria australia abstract combined hydrogeological and hydrogeochemical data allow flow systems and the origins of solutes in the honeysuckle creek area of the southeastern murray basin which is an area affected by dryland salinity to be constrained recharge occurs both on the uplands that are composed of fractured violet town volcanic rocks and the riverine plain that comprises sediments of the shepparton and coonambidgal formations groundwater from the violet town volcanics has low salinity 20 mmol l groundwater has intermediate cl br ratios 600 1000 which indicate that the high salinities do not simply result from halite dissolution rather mixing of groundwater homogenises cl br ratios and evaporation as a consequence of a shallow water table is the dominant process that increases salinity oxygen and h isotopes also indicate that mixing and evaporation have occurred these results indicate that land use over the whole region not just the uplands needs to be considered in any salinity management plans additionally future development of salinity is controlled by depth to the water table on the plains and the efficiency of recharge rather than by salt stores halite or brines in the unsaturated zone

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

chlorine 36 in groundwater as a palaeoclimatic indicator the east midlands triassic sandstone aquifer uk the36cl contents of groundwaters from the east midlands triassic sandstone have been used to deduce rainfall its chloride content and evapotranspiration during the late pleistocene at this time the regional precipitation and evapotranspiration would have been reduced relative to the modern and holocene climate it is estimated that the infiltration was reduced by about 40 mm a 1 the method for evaluation of these palaeoclimatic parameters is dependent upon the major cl source being a marine aerosol fall out this is the general case but groundwater east of the exploited zone of the aquifer contains chloride which is derived from saline formation water with a marinecl br ratio and in equilibrium with the in situ neutron flux the fall out of cosmogenic36cl at the geomagnetic latitude 56 2 n is evaluated as 30 6 atoms m 2s 1 and is significantly greater than that estimated from the theoretical fall out curve of bentley et al 1 the bomb peak of36cl remains entirely within the unconfined zone of the aquifer the assessment of groundwater residence time from the36cl chronometer is shown to be impossible for this aquifer

dissolved oxygen and nitrate of groundwater in choshui fan delta western taiwan dissolved oxygen do and nitrate concentrations of groundwater from a total of 191 new monitoring wells with a maximum depth up to 300 m in the choshui fan delta of taiwan were measured to delineate the regional patterns of the two components unconfined aquifers of the proximal part of the fan delta contain 1 7 mg l of do and a 250 m deep well still has an unusual value of 1 83 mg l do concentrations decrease downgradient along flow paths to below detection limit 0 01 mg l in shallow confined aquifers during the last 40 years possibly due to oxidation of organic matters in sediments a plume of high nitrate n concentrations 0 5 17 mg l originating from the proximal part of the fan delta has been developing possibly since 1956 due to agricultural fertilizers from 1997 to 2001 the concentration has increased at a rate of ca 0 28 mg l per year

chemical and isotopic o h c composition of surface waters in the catchment of lake donggi cona nw china and implications for paleoenvironmental reconstructions abstract the oxygen hydrogen and carbon isotope ratios and major and trace element concentrations of surface waters are reported for the catchment of lake donggi cona qinghai province china the chemistry of the surface waters in the southeastern catchment is reflecting the dissolution of carbonate rocks whereas thermal waters add sodium and chlorine to the waters in the northern catchment the dongqu river draining the southeast catchment contributes 87 to 94 to the water budget of the lake thermal waters and waters from the northern catchment add 6 to 13 the combination of hydrogen and oxygen isotopes provides evidence that only small amounts of recycled lake water contribute to the precipitation in the catchment most of the moisture may be transported by the east asian summer monsoon or an eastern branch of the south asian monsoon into the donggi cona region from oxygen isotope ratios it is calculated that about 45 of the lake water input is evaporated and 55 leaves the lake through a channeled outflow the carbon isotope ratios identifies microbial respiration of organic matter probably in soils and sediments of the catchment as the major source of dissolved inorganic carbon in most surface waters and the lake an isotope effect from biological processes in the lake is minor and can be neglected in order to explain isotope ratios of inorganic carbon in lake water the results imply that oxygen isotope ratios in the lake sediment archives mainly mirror the relation between precipitation and evaporation p e which may be controlled by changes in the global water cycle like monsoon intensity or by tectonically driven local changes affecting the outflow flux a comparison between lake archives based on ostracod shells and the modern system indicates similar 18o values for the lake water since 4 3 ka but different 13cdic values this discrepancy between carbon isotope ratios in ostracod shells and modern lake water samples may be due to thermal waters with high 13cdic emerging near the coring site it is suggested that carbon isotopes of ostracods from a sediment drill core reflect the activity of a local thermal spring at the lake bottom whereas oxygen isotopes provide evidence for an open lake system since about 11 ka and that the climate and environment of the donggi cona region changed very little over the last 4300 years

discussion on low grade metamorphism of the welsh basin lower palaeozoic succession and example of diastathermal metamorphism reply by r e bevins and d robinson

the relationship between and evolution of surface water and groundwater in songnen plain northeast china to improve water management the relation and the hydrochemical evolution of surface water and groundwater were studied in the songnen plain the surface water and groundwater samples were evaluated for stable isotopes and hydrochemistry analyses the stable isotopic compositions 18o d indicate the groundwater recharges from the precipitation however the connectivity between surface water and groundwater is weak because of the clay layer and the interrupted aquifer the water evolution is from ca mg hco3 to na hco3 by the evaporation water rock interaction and ion exchange processes the water evaporation and leaching of saline alkaline soil are the main reasons for water salinity further the leaching of salts in the soil during recharging from backwater and irrigation water intensifies the salinization the relationship between and evolution of surface water and groundwater provide important guidance for water management not only in the arid and semi arid area but also in the soda saline alkali soil regions of the world

groundwater evolution in the continental intercalaire aquifer of southern algeria and tunisia trace element and isotopic indicators abstract the geochemical processes taking place along an 800 km flow line in the non carbonate continental intercalaire aquifer ci aquifer in north africa are described using chemical major and trace element and isotopic indicators the aquifer is hydraulically continuous from the atlas mountains in algeria to the chotts of tunisia and the geochemical evidence corroborates this the highest discharge temperature is 73 c but silica geothermometry indicates a maximum temperature of 94 c at depth chloride concentrations increase from 200 to 800 mg l 1 and the br cl ratios confirm the dissolution of non marine evaporites or interstitial waters as the main source of salinity fluoride concentrations are low and are likely to be derived from rainfall recording oscillations in source radiocarbon ages except near outcrop are at or near detection limits and the 18o and 2h values indicate a cooler recharge regime with rainfall having lower primary evaporation than today this is shown by the fact that mean isotope ratios of ci waters are around 3 lighter than the present day weighted mean value for rain major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy uniform evolution with continuous water rock interaction takes place along the flow lines which are only disturbed near the tunisian chotts by groundwater converging from additional flow lines the ageing of the water can also be followed by the smooth increase in several indicator elements such as li k and mn which are least affected by solubility controls similarly the influence of marine facies in the tunisian sector may be recognised by the changing mg ca and higher br cl as well as trace element indicators the groundwaters are oxidising up to 300 km from outcrop dissolved o2 has persisted for at least 20 ka and within this zone the concentrations of several elements forming oxy anions such as u and cr increase and no3 remains conservative beyond 300 km from outcrop the groundwaters are reducing and contain high fe concentrations the basin contains huge reserves of fresh brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super saturation caused during abstraction as well as high concentrations of some harmful elements such as cr in the oxidising section

origin of mountains on io by thrust faulting and large scale mass movements voyager stereoimages of euboea montes io indicate that this mountain formed when a large crustal block was uplifted 10 5 kilometers and tilted by approximately 6 degrees uplift triggered a massive slope failure on the northwest flank forming one of the largest debris aprons in the solar system this slope failure probably involved relatively unconsolidated layers totaling approximately 2 kilometers in thickness overlying a rigid crust or lithosphere at least 11 kilometers thick mountain formation on io may involve localized deep rooted thrust faulting and block rotation due to compression at depth induced during vertical recycling of io s crust

chemical evolution of groundwater in the river danube deposits in the southern part of the pannonian basin hungary processes controlling the groundwater chemical composition were studied in the river danube deposits in the southeastern part of hungary phreeqm a combined geochemical and one dimensional transport model and phreeqe netpath and wateqf geochemical computer codes were used to simulate these processes the main processes controlling water chemistry are equilibrium with calcite undersaturation in dolomite and albite weathering in the recharge area ion exchange along the flow path and ion exchange and mixing with old water at the end of the flow path ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied isotopic data support the geochemical model the groundwater ages adjusted for the modeled c mass transfer range from 3300 to 20 200 a b p cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred this displacement is attributed to tectonic and paleoclimatic events at the end of the pleistocene

provenance and fate of arsenic and other solutes in the chaco pampean plain of the andean foreland argentina from perspectives of hydrogeochemical modeling and regional tectonic setting extensive arsenic as enriched groundwater is known to occur in the aquifers of the chaco pampean plain of argentina previous studies speculated that the as mobilization in these groundwaters was a direct result of their elevated ph and oxidative conditions the volcanic glass layers present in the aquifer matrix were hypothesized as one of the possible sources of as to the groundwaters here we examine the groundwater chemistry of the santiago del estero province of chaco pampean plains of argentina and test these hypotheses by using hydrogeochemical modeling within the framework of the regional geologic tectonic setting the study area is located in the active foreland of the andean orogenic belt which forms a continental arc setting and is dotted with several hot springs rhyolitic volcanic glass fragments derived from arc volcanism are abundant within the aeolian fluvial aquifer sediments and are related to the paleo igneous extrusion in the vicinity hydrogeochemical analyses show that the groundwater is in predominantly oxidative condition in addition some of the groundwaters exhibit very high na cl and so42 concentrations it is hypothesized in this study that the groundwater chemistry has largely evolved by dissolution of rhyolitic volcanic glass fragments contained within the aquifer sediments along with mixing with saline surface waters from adjoining salinas which are thought to be partially evaporated remnants of a paleo inland sea flow path modeling stability diagrams and thermodynamic analyses undertaken in this study indicate that the dominant evolutionary processes include ion exchange reactions chemical weathering of silicate and evaporites in monosialitization dominated weathering geochemical modeling predicts that plagioclase feldspar and volcanic glass are the major solids phases that contribute metal cations and dissolved silica to the local groundwaters co influxed oxyanions with similar ionic radii and structure e g mo si v po43 compete with as for mineral surface site leading to as mobilization to the groundwaters without considering the influence of microbial activities further the transition of the ca rich groundwater to na rich groundwater by mixing with water from the salinas and or evaporative concentration might also have led to counter ion effects a type of ion exchange reactions and hence further enrichment of groundwater by as some of the as may also have been contributed from mixing of meteoric water with magmatic sourced water in the geothermal springs

a transmission electron microscope study of white mica crystallite size distribution in a mudstone to slate transitional sequence north wales uk high resolution transmission electron microscopy hrtem measurements of the thickness of white mica crystallites were made on three pelite samples that represented a prograde transition from diagenetic mudstone though anchizonal slate to epizonal slate crystallite thickness measured normal to 001 increases as grade increases whereas the xrd measured 10 a peak profile the kubler index decreases the mode of the tem measured size population can be correlated with the effective crystallite size n 001 determined by xrd the results indicate that the kubler index of white mica crystallinity measures changes in the crystallite size population that result from prograde increases in the size of coherent x ray scattering domains these changes conform to the scherrer relationship between xrd peak broadening and small crystallite size lattice strain broadening is relatively unimportant and is confined to white mica populations in the diagenetic mudstone rapid increases in crystallite size occur in the anchizone coincident with cleavage development changes in the distribution of crystallite thickness with advancing grade and cleavage development are characteristic of grain growth by ostwald ripening the kubler index rapidly loses sensitivity as an indicator of metapelitic grade within the epizone

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

gigantic paleolandslide associated with active faulting along the bogd fault gobi altay mongolia on the basis of analyses of satellite imagery aerial photographs and field observations we describe the occurrence of one of the largest paleolandslides 50 km3 ever recognized in an intracontinental domain the slide occurred along the active bogd fault in the gobi altay mountain range in mongolia morphological and structural analyses of the relationships between the landslide and the area affected by active tectonics suggest that this gigantic mass movement was associated with surface faulting during a strong earthquake

occurrence of molybdenum in british surface water and groundwater distributions controls and implications for water supply data for mo in british surface water and groundwater collated from a number of databases show that concentrations are in most cases low of the order of 2 g l or less however variability is large and sporadic high values are found in both streamwaters and groundwaters data for some 11 600 british streamwater samples indicate a 10 90th percentile range of 0 08 2 44 g l with a median of 0 57 g l and maximum observation of 230 g l high values tend to be from streams on clay rich formations and sulphide mineralised bedrock and streams affected by localised urban and industrial contamination monitored lowland river waters also typically have median concentrations 1 g l although higher values are present in a number of urban industrialised english rivers highest observed concentrations median 20 g l occur under low flow conditions in a river system from an urban industrial area of ne england and are likely the products of industrial contamination and mine drainage concentrations in 96 upland lakewater samples from nw england are universally 0 1 g l or less data for 1735 groundwater samples from across britain have a 10 90th percentile range for mo of 0 035 1 80 g l with a median of 0 20 g l and maximum observation of 89 g l relatively high values derive from some lower cretaceous greensand carboniferous limestone and mudstone coal measures aquifers particularly under anaerobic conditions release from fe oxides and possibly mn oxides by reductive dissolution is a likely mechanism for the concentrations under more rarely observed sulphate reducing conditions in british aquifers concentrations of mo diminish likely due to sequestration by precipitating sulphide minerals the observed ranges in aqueous samples indicate that most water sources in britain have mo concentrations more than an order of magnitude below the who health based value for mo in drinking water 70 g l such sources are unlikely to pose a risk to drinking water from the current who guidance provided those impacted locally by mining or other industrial contamination are avoided

stability assessment of himalayan road cut slopes along national highway 58 india himalaya is one of the most tectonically and seismically active mountain chains in the world having complex geological and geotechnical conditions the himalayan region experiences frequent slope failure posed due to various natural and anthropogenic causes slope instability issues have consequent effects on the socio economic development of the people and the region in a large scale in the present study stability analysis of vulnerable road cut slopes along nh 58 from rishikesh to devprayag in the lesser himalayas has been conducted critical slopes were identified by considering the geological and the geotechnical complexities within the region rock mass characterisation techniques have been employed for slope stability assessment rock mass rating rmr slope mass rating smr and continuous slope mass rating csmr methods have been applied to evaluate different stability levels of rock mass along the highway spatial variation of stability classes using rmr smr and csmr techniques has been analysed on geographic information system gis tool kinematic analysis technique was also employed to identify the different modes of structurally controlled failures in jointed rock mass accordingly remedial measures have been suggested to improve slope stability

origin of nickel in water solution of the chalk aquifer in the north of france and influence of geochemical factors in the north of france high registers of nickel are sometimes recorded within the chalk aquifer in a confined context the presence of pyrite in the covering clays or in the marcasite nodules encrusted in the clay may constitute a natural source of trace metals with an objective of sanitary control the limits of chemical contents regulating the quality of water destined for human consumption have been lowered by the european framework directive in the field of water policy 2000 60 ec as a result nickel limits have been reduced from 50 to 20 g l the analyses carried out on three water catchment fields in our area of study were centred on variable parameters eh o2 d ph conductivity t major elements so4 no3 and metals fe ni mn co the acquired data enabled us to identify from one hand the conditions which are presented within the site special thanks to the evolution of nitrate and iron contents and on the other hand the natural origin geological of nickel for two of the three sites studied based essentially on the evaluation of the nickel cobalt ratio thus on the first site the evolution of nickel content and nitrate content showed the influence of the phenomenon of denitrification on the re mobilisation of the nickel whereas on the second site a high variation of total iron content and oxygen dissolved in solution highlighted a particular phenomenon of oxidation of the pyrite through molecular oxygen finally the correlation with the sulphates clearly showed behaviour of the nickel once released that was entirely dependent on the phenomenon of adsorption on the iron and manganese hydroxides

multiphase reddening and weathering events in upper carboniferous red beds from the english west midlands sediments of the halesowen and salop formations westphalian d stephanian in the west midlands were deposited on the southern margin of the pennine basin during a period of relative tectonic quiescence during the variscan orogeny the clastic framework of the predominantly red sandstones and mudstones in the salop formation includes large detrital hematite grains these yield a primary component of magnetization indicating that sediments were deposited close to the carboniferous palaeo equator variscan uplift erosion and subsequent deep oxidation in an arid climate during the permian resulted in the precipitation of finer hematite in rocks of both formations which are now found at depths of over 150 m below the present day ground level these grains carry secondary magnetizations which indicate formation at palaeolatitudes of between 5 and 15 n the position that britain occupied during the permian the pattern of permian remagnetization particularly in borehole samples suggests that the secondary fine grained hematite was precipitated as a result of lateral flow of meteoric water through connected permeable sandstone units rather than downward percolation through the entire succession present day surface weathering has resulted in the dissolution of the finer grains of hematite and in some cases where permeabilities are relatively high it has also affected the coarser fraction consequently the record of late carboniferous and permian magnetization events is commonly incomplete in strata close to the present day ground level