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

identifying the origin of groundwater samples in a multi layer aquifer system with random forest classification summary accurate identification of the origin of groundwater samples is not always possible in complex multilayered aquifers this poses a major difficulty for a reliable interpretation of geochemical results the problem is especially severe when the information on the tubewells design is hard to obtain this paper shows a supervised classification method based on the random forest rf machine learning technique to identify the layer from where groundwater samples were extracted the classification rules were based on the major ion composition of the samples we applied this method to the campo de cartagena multi layer aquifer system in southeastern spain a large amount of hydrogeochemical data was available but only a limited fraction of the sampled tubewells included a reliable determination of the borehole design and consequently of the aquifer layer being exploited added difficulty was the very similar compositions of water samples extracted from different aquifer layers moreover not all groundwater samples included the same geochemical variables despite of the difficulty of such a background the random forest classification reached accuracies over 90 these results were much better than the linear discriminant analysis lda and decision trees cart supervised classification methods from a total of 1549 samples 805 proceeded from one unique identified aquifer 409 proceeded from a possible blend of waters from several aquifers and 335 were of unknown origin only 468 of the 805 unique aquifer samples included all the chemical variables needed to calibrate and validate the models finally 107 of the groundwater samples of unknown origin could be classified most unclassified samples did not feature a complete dataset the uncertainty on the identification of training samples was taken in account to enhance the model most of the samples that could not be identified had an incomplete dataset

an isotopic study 2h and 18o of water movements in clayey soils under a semiarid climate we applied the natural variations of stable isotopes in water to the study of infiltration in clayey soils and to the study of groundwater recharge in the small drainage basin of barogo in west africa the comparison between the variations in isotopic contents of soil water and rainwater in 1988 and 1989 led us to characterize two infiltration processes 1 an infiltration through the soil matrix of rainwater that mixed with mobile water which was held in the superficial part of the soil and was enriched in heavy isotopes by evaporation and 2 a fast and deeper infiltration by preferential flow along macropores that bypassed the superficial part of the soil the study of the variations in groundwater isotopic content led us again to separate the recharge process into two components 1 a slow infiltration through the soil matrix and the weathered basement distributed recharge and 2 a fast and direct recharge through conducting fissured zones localized recharge a schematic and local representation of groundwater recharge in the barogo basin allowed us to estimate that direct recharge represented around 70 of the total recharge in 1989

chemical multi isotopic li b sr u h o and thermal characterization of triassic formation waters from the paris basin this work reports chemical and isotope data and temperature estimates for seven water samples collected from triassic formations in the paris basin in france four samples were collected in the central part of the basin saline waters and three were collected at the edge of the basin near the recharge zone dilute waters the saline waters collected from the chaunoy and champotran boreholes have high salinities around 120 g l and very similar chemical and isotopic compositions the saline water sample from the la torche borehole has much higher salinity 168 g l and significantly different isotope characteristics the chemical geothermometers applied to these fluids from the centre of the basin give temperature values ranging between 80 and 100 c the fresh water samples collected at the edge of the basin have very different chemical and isotopic compositions these dilute water samples santenay and ch teauroux are shallow with colder temperatures of around 45 to 50 c the study of uranium activity ratios for these triassic formation waters allows us as a first approximation to estimate a mean apparent fluid circulation velocity of around 0 2 m yr which corresponds to a mean age slightly higher than 1 my for waters sampled in the chaunoy champotran and la torche fields in the centre of the basin the multi isotope characterization of triassic formation waters shows that our data are in agreement with literature values as concerns traditional isotope systematics delta18o deltad 87sr 86sr li and b isotope signatures in the centre of the paris basin are in a good agreement with a fluid signature derived mainly from water rock interactions involving clastic rocks with water essentially resulting from a seawater derived brine endmember diluted by meteoric waters the data reported in the present work for li and b isotopes could be used as a reference for future studies to characterize sandstone formation waters

late pleistocene and holocene large magnitude earthquakes along himalayan frontal thrust in the central seismic gap in nw himalaya kala amb india abstract the himalayan frontal thrust hft forms the southernmost active tectonic mountain front of the himalaya to understand the ongoing tectonics further paleoseismological study has been carried out in the vicinity of the hft system along the himalayan front near kala amb india the trench excavation survey conducted across an explicit surface exposure of the hft exhibits two distinct faults considered to be associated with the reactivation of the hft where the middle siwalik rocks late miocene have repeatedly thrust over the late pleistocene and holocene sediments presence of large sized coseismically induced sand injection feature and its disposition recognized in the trench also suggest occurrence of large magnitude earthquakes in this region an uplifted and upwarped strath terrace 3 to 5 m thick alluvium resting over the 15 m high middle siwaliks abruptly truncated by the hft indicates its latest activity optically stimulated luminescence dating techniques were employed to constrain the chronology of events the long term slip rate of the abandoned terraces due to the activity of the hft is estimated to be 3 4 mm yr or greater since late holocene the paleoseismological investigations have provided unambiguous evidences of at least two large magnitude earthquakes occurred in this region where an earthquake with 12 m or larger surface displacement and magnitude 7 5 or greater hit this region in the period between 29 3 ka and 17 ka in the late pleistocene and another great earthquake recurred with 20 22 m or more surface displacement and magnitude of 7 7 or greater between 5 8 ka and 2 ka in the holocene the present study is the first time report of multiple large magnitude paleoearthquakes in the northwestern part of the frontal himalaya during late pleistocene and holocene the repeated reactivation of hft substantiates high seismic potential of the frontal himalaya and calls for more extensive study of paleoearthquakes of this vastly populous mountainous region

groundwater recharge and evolution in the dunhuang basin northwestern china groundwater recharge and evolution in the quaternary aquifer beneath the dunhuang basin was investigated using chemical indicators stable isotopes and radiocarbon data to provide guidance for regional water management the quality of groundwater and surface water is generally good with low salinity and it is unpolluted the dissolution of halite and sylvite from fine grained sediments controls concentrations of na and k in the groundwater but na cl molar ratios 1 in all samples are also indicative of weathering of feldspar contributing to excess na the dissolution of carbonate minerals yields ca2 to the groundwater thereby exerting a strong influence on groundwater salinity the delta o 18 and delta h 2 values in unconfined groundwater are enriched along the groundwater flow path from sw to ne in contrast confined groundwater was depleted in heavy isotopes with mean values of 10 4 parts per thousand delta o 18 and 74 4 parts per thousand delta h 2 compared with the precipitation values all of the groundwater samples were strongly depleted in heavy isotopes indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited the unconfined water is generally young with radiocarbon values of 64 9 79 6 pmc in the northern basin radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of similar to 15 ka indicates that this groundwater was recharged during a humid climatic phases of the late pleistocence or early holocene the results have important implications for inter basin water allocation programmes and groundwater management in the dunhuang basin c 2012 elsevier ltd all rights reserved

hydrogeochemical and isotopic characterization of the groundwater in the chari baguirmi depression republic of chad the chari baguirmi groundwater in the republic of chad is undergoing a steady deterioration both qualitative and quantitative due to climatic severe droughts and anthropogenic overexploitation constraints however this major water resource has not been to date the object of any comprehensive scientific investigation to fill this gap and consider a sustainable exploitation a hydrodynamic and hydrochemical study was undertaken this aquifer is located south of lake chad and displays a significant natural piezometric depression piezometric campaign on an area of 70 000 km2 bounded by lake chad the chari river the mountains of guera and the dunes of harr was conducted to understand the hydrodynamics of the groundwater water samples were collected on 124 points scattered over the study area hydrochemical and isotopic analyses 18o and 2h were achieved on all samples the interpretation of hydrochemical data was done using the piper diagram the multivariate analysis hierarchical ascending classification the index of base exchanges and ratios of na cl na so4 cl so4 br cl sr ca the hydrochemical results coupled with groundwater isotopes data allowed to understand the processes that govern the mineralization and the origin of groundwater salinity these investigations allowed on the one hand to differentiate between two poles of water mixing and second to demonstrate that the mineralization process and origin of salinity in the center of depression are both related to the lithology of the geological formations crossed by groundwater flow and climatic events causing evaporation of water from the aquifer

hydrological factors in the interpretation of stable isotopic proxy data present and past a european perspective in the context of this paper stable isotopic proxies are those preserving directly or via known or calculable fractionation factors a record of 18o 16o and or 2h 1h in the water which contributed to their growth suitable proxies include amongst others tree ring cellulose bone phosphate lake sediment minerals and speleothem fluid inclusions a principal aim of studying isotopic proxies is to gain more information about past climates through a knowledge of how rainfall isotope compositions have changed over time however converting back from proxy to rainfall is not necessarily straightforward because however well the isotopic fractionation due to proxy growth or formation is understood a variety of modifying processes may have intervened between this and the actual rainfall events three main reservoirs of environmental water may contribute to the isotopic compositions of terrestrial proxy indicators surface waters soil moisture and groundwater each of these can in principle be isotopically modified compared to rainfall in the locality this review examines these effects and how they may change under different european climate types at the present day it is concluded that while groundwater isotopic compositions typically represent closely the bulk composition of rainfall under a variety of climatic regimes soil and particularly lake waters require detailed study if their isotope systematics are to be adequately understood the review also finds that to a large extent the present is the key to the past in terms of recharge processes during the late pleistocene though glaciation may have had profound isotopic consequences in certain areas while a more general aridity led to the apparent absence of recharge in most areas for much of the late devensian

influence of matrix diffusion and exchange reactions on radiocarbon ages in fissured carbonate aquifers the parallel fissure model coupled with the equation of diffusion into the matrix and with exchange reaction equations has been used to derive a simple formula for estimating the influence of matrix porosity and reaction parameters on the determination of radiocarbon ages in fissured carbonate rocks examples of evidently too great radiocarbon ages in carbonate formations which are not explainable by models for the initial sup 14 c corrections can easily be explained by this formula parameters obtained for a chalk formation from a known multitracer experiment combined with a pumping test suggest a possibility of sup 14 c ages more than three orders of magnitude greater than the ages which would be observed if the radiocarbon transport took place only in the mobile water in the fissures it is shown that contrary to the solute movement on a small scale and with a variable input the large scale movement characteristic for the sup 14 c dating does not necessarily require the knowledge of kinetic parameters because they may be replaced by the distribution coefficient discordant tritium and sup 14 c concentrations are commonly interpreted as a proof of mixing either in the aquifer or at the discharge site for fissured carbonate formations however anmore alternative explanation is given by the derived model showing a considerable delay of sup 14 c with respect to nonsorbable tracers less

estimation of evapotranspiration losses in the vadose zone using stable isotopes and chloride mass balance method this study used stable isotope and chloride data of porewater to evaluate water fluxes through the vadose zone and thereby estimate evapotranspiration water losses in parts of the nabogo catchment of the white volta basin in ghana the overall objective was to develop a framework so that the recharge regime can be properly conceptualized for numerical hydrological modeling unsaturated zone material was sampled at regular intervals of 50 cm to a maximum depth of 300 cm in four different locations in the study area rainwater groundwater and surface water were simultaneously sampled and analyzed for their 18o and 2h characteristics porewater extracted from the unsaturated zone material was analyzed for the 18o and 2h and chloride content and profiles were created to gauge the isotopic evolution of precipitation and estimate evaporative losses at each interval of the sampling the chloride mass balance technique was used to estimate the fraction of infiltrating water remaining at each interval of the sampling transpiration losses through the entire profile were then estimated this study finds that the vertical infiltration of water through the vadose zone is dominated by piston flow and a mixture of piston and preferential flows in the shallow subsurface 0 0 3 0 m evaporative losses estimated from stable isotope data fall in the range of 29 3 52 4 322 3 576 4 mm year of the annual precipitation with an average of 40 or 440 mm year estimated vadose zone recharge at the maximum depth of sampling ranges between 11 1 and 185 mm year with an average of 32 9 mm year representing 1 1 18 5 and 3 29 of the annual precipitation respectively estimated transpiration losses within this interval range between 29 1 290 mm year and 69 5 695 mm year with an average of 54 7 547 mm year of the annual precipitation transpiration losses appear to increase down the profile and apparently account for a significant percentage of water losses in the vadose zone a significant proportion of the original precipitation is lost within the upper 300 cm 3 m of the vadose zone the water table fluctuations method was independently used to estimate saturated zone groundwater recharge and indicates that recharge rates range between 64 65 and 151 2 mm year with an average of 102 5 mm year which respectively represent 5 9 13 7 and 9 3 of the average annual precipitation in the area the apparently higher estimates from the water table fluctuations method may arise from uncertainties in the specific yield values used for the vadose zone material

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

late pleistocene precipitation δ18o interpolated across the global landmass global water cycles ecosystem assemblages and weathering rates were impacted by the 4 c of global warming that took place over the course of the last glacial termination fossil groundwaters can be useful indicators of late pleistocene precipitation isotope compositions which in turn can help to test hypotheses about the drivers and impacts of glacial interglacial climate changes here a global catalog of 126 fossil groundwater records is used to interpolate late pleistocene precipitation 18o across the global landmass the interpolated data show that extratropical late pleistocene terrestrial precipitation was near uniformly depleted in 18o relative to the late holocene by contrast tropical 18o responses to deglacial warming diverged late pleistocene 18o was higher than modern across india and south china but lower than modern throughout much of northern and southern africa groundwaters that recharged beneath large northern hemisphere ice sheets have different holocene pleistocene 18o relationships than paleowaters that recharged subaerially potentially aiding reconstructions of englacial transport in paleo ice sheets global terrestrial late pleistocene precipitation 18o maps may help to determine 3 d groundwater age distributions constrain pleistocene mammal movements and better understand glacial climate dynamics

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

monitoring termination ii by environmental magnetic records from subtropical south atlantic sediments termination ii the transition from oxygen isotope substages 6 2 to 5 5 at around 130 ka is the penultimate drastic change from extreme glacial to interglacial climatic conditions invoking shifts in terrigenous and biogenous influx to the deep ocean environmental magnetic methods are applied to reveal these shifts in an ocean spanning transect of the subtropical south atlantic magnetic mineralogy grain size and coercivity reflect intensified eolian inflow of volcanogenic material from the andes due to enhanced continental aridity and wind intensity during substage 6 2 an african dust supply is only observable in continental vicinity on the santos plateau magnetic attributes indicate fluvial influx of eroded flood basalts layers of reductive magnetic mineral diagenesis were identified only at the westernmost sites and appear to reflect paleoredox boundaries related to enhanced corg deposition at the termination and during stage 5 5 in all unaltered sections stage 5 5 is magnetically similar to the holocene

fuzzy c means cluster analysis of early diagenetic effects on natural remanent magnetisation acquisition in a 1 1 myr piston core from the central mediterranean abstract the influence of early diagenesis on the natural remanent magnetisation nrm in sediments from the calabrian ridge central mediterranean is analysed with the help of fuzzy c means fcm cluster analysis and non linear mapping nlm the sediments are variably coloured white beige purplish greenish and grey layers occur with occasionally intercalated sapropels the nrm acquired depends on both depositional conditions and diagenetic processes to describe these fcm was performed with in arm caco3 ba mn and s as variables an eight cluster model was derived with the clusters belonging to two categories one expressing mainly diagenetic processes i e dissolution and precipitation and the other expressing mainly depositional conditions the impact of diagenesis on nrm acquisition is profound and not restricted to the close vicinity of the anoxic sapropelitic layers as a consequence the influence of diagenetic processes on the nrm should be thoroughly assessed when selecting samples e g for the determination of the relative palaeointensity of the geomagnetic field application of multivariate classification techniques appears to be useful because it links rock magnetic parameters to the geochemical environment in the present piston core three short reversed geomagnetic events in the brunhes chron are preserved and indeed occur in clusters expressing no or minor diagenesis the recording of the blake event however has been prevented by later precipitation of magnetite in the corresponding interval

dissolved gas paleotemperatures and 18o variations derived from groundwater near uitenhage south africa abstract under the near ideal hydrologic conditions provided by the uitenhage artesian aquifer reliable estimates of paleotemperatures were obtained by measurement of the dissolved n2 and ar in groundwater confidently dated in the range 28 000 yr b p to the present using 14c the mean annual air temperature in this area during the last glaciation is calculated to have been on average 5 1 2 c lower than during the holocene the change in the 18 o 16 o ratio of the groundwater corrected for changes in ocean water amounted to 0 4 per c

radiocarbon dating of groundwater of the aquifer confined in the lower triassic sandstones of the lorraine region france abstract blavoux b and olive ph 1981 radiocarbon dating of groundwater of the aquifer confined in the lower triassic sandstones of the lorraine region france in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 167ndash 183 stable isotope and groundwater chemistry analyses on samples from about 40 boreholes in the lorraine region eastern france are used to evaluate the paleohydrological regime of the lower triassic sandstone aquifer in the study of the mechanisms of the general water dynamics of the aquifer at present in this sandstone aquifer the estimation of the 14 c activity a 14 in the total dissolved carbon tdc to 100 of modern carbon is justified by the absence of carbonates in the reservoir and by the 13 c contents in the tdc a significant relation could be determined between the 14 c activity in the tdc and 13 c a 14 7 7 13 59 6 this gradual enrichment of the tdc with 13 c results from the escape of the dissolved co 2 the meaning of the radiometric age is discussed as a function of piston and exponential type flows the study of the stable isotopes 18 o and 2 h revealed two water families the most recent waters have 18 o values higher by 1 0 than the more than 10 4 yr old waters this 1 0 discontinuity corresponds to the improvement of weather conditions during the holocene which amounts to 2 5 c the isochrons of the aquifer reveal the existence of hydrogeological sections bounded by faults where the rates of circulation are different

palaeorecharge conditions of the deep aquifers of the northern aquitaine region france summary the study was carried out in the northern part of the aquitaine basin extending in southwest france the basin has been intensively exploited for various purposes for many years although the geological context is well known there are still some gaps in the knowledge about the hydrogeochemical regime groundwater average residence time and the palaeohydrological conditions prevailing during the recharge period which would help to secure sustainable exploitation of the resources environmental isotopes 18 o 2 h 3 h 13 c together with radiocarbon were used to evaluate hydrochemical evolution residence time and palaeorecharge conditions for jurassic cretaceous and eocene aquifers radiocarbon activity in the aquifers varies widely between 0 and 94 pmc after radiocarbon corrections the ages indicate both modern and old waters sometimes exceeding the limit for 14 c dating the fontes and garnier model is best adapted to the specificity of the carbonate system the content in stable isotopes of water is varying between 7 7 and 4 9 for 18 o and 52 3 to 29 6 for 2 h the wide ranges of stable isotopic values imply variable climatic conditions a group of isotopically depleted samples was detected indicating colder climatic conditions during the recharge radiocarbon ages calculation together with isotopic signature point out that the depletion in stable isotopic values fits the period between 20 and 15 ka b p and therefore indicate the last glacial maximum lgm according to the correction model the transition from pleistocene to holocene would occur between 15 and 12 ka b p palaeohydrological data from the northern aquitaine basin does not confirm a significant hiatus in the recharge history the recharge conditions in south europe seem to have occurred under discontinuous permafrost conditions as documented by many palaeoclimatological archives this is in favour of an uninterrupted recharge of the confined aquifers of northern aquitaine basin such information should be considered by modellers in their attempts to simulate the hydrogeological functioning of large confined aquifers on the very long time range

carbon isotopes to constrain the origin and circulation pattern of groundwater in the north western part of the bohemian cretaceous basin czech republic abstract the bohemian cretaceous basin represents a complex hydrogeological system composed of several aquifers with very favourable hydrogeological properties these aquifers have been exploited for many years the sustainability of such resources might be guaranteed by well organised water management which requires a detailed knowledge about the functioning of the hydrogeological system although many efforts have previously been made to evaluate groundwater residence time the many intricate geochemical processes complicate groundwater dating the current study clarifies the functioning of this complex hydrogeological basin using hydrogeochemical and isotopic investigations chemical data and a combination of 13 c and 14 c isotopes within the cenomanian and the turonian layers indicate groundwater interactions with deep seated co 2 rock matrix surface waters and fossil organic matter very depleted 13 c values average 13 c 13 4 suggest interactions with fossil organic matter whereas enriched values account for the interaction with deep co 2 gas ascending from the upper mantle via the numerous faults and fractures and also to a lesser extent from calcite dissolution geochemical processes that take place in the system cause a clear depletion in 14 c that greatly complicates groundwater residence time evaluation different dilution correction models have been applied considering the different c origins the stable isotope content mainly 18 o values indicates both the contribution of modern precipitation and the partial infiltration of palaeowaters during colder climatic conditions from the end of the pleistocene the apparent 14 c groundwater ages range from modern to 11 1 ka bp which suggests some post glacial infiltration from melting ice sheets finally all the acquired information was used to propose a conceptual model of c origin within the basin

peru basin sediments diagenetic implications of a low coercivity overprint of the nrm two coexisting populations of magnetite that vary by at least 320 kyr in age characterize the magnetomineralogy in oxic through suboxic peru basin sediment 7 04 s 88 28 w 1 primary magnetite barely underwent post depositional alteration and yields a straightforward magnetostratigraphy brunhes chron top of olduvai subchron 2 a stable low coercivity overprint of the nrm resides in secondary slightly oxidized sd magnetite that recorded the brunhes chron direction the secondary magnetite appears at the modern fe redox boundary 2 6 mbsf and continues downhole to abruptly disappear at 5 3 mbsf in the matuyama chron it can be discerned by combined analyses of directional data and the verwey transition in low temperature remanence measurements 20 300 k that appears concomitant with the overprint

regional variations in tectonic geomorphology along a segmented convergent plate boundary pacific coast of costa rica abstract pacific coastal mountain piedmont landforms of costa rica extend across the tectonic boundary between the forearc and magnetic arc region of an active convergent margin this plate boundary became segmented circa 1 million years ago when the aseismic cocos ridge impinged upon the middle america trench offshore from the southernmost coastal area of costa rica morphometric analyses of 100 mountain fronts and numerous river long profiles radiometric dating and field studies were conducted in two study areas located arcward from the plate boundary where oceanic lithosphere of the cocos plate is being subducted beneath the caribbean plate region i and the partially subducted aseismic ridge is uplifting the plate margin by isostatic and collisional processes region ii values of tectonic geomorphic parameters mountain front sinuosity s percent dissected facets ffd river concavity k are not only different statistically in regions i and ii but are also different in the areas experiencing isostatic and collisional responses to the subducting aseismic ridge in the area experiencing collisional responses mountain fronts developed along ne dipping imbricate thrust and high angle reverse faults step upward and inland from the coast morphometric data along with the divergence of river terrace profiles from the coast piedmont inland toward the mountains indicates higher uplift rates along interior range mountain fronts isostatic uplift in the outer forearc area in region ii produces a distinctly different morphologic and neotectonic style characterized by regional uplift distributed across a number of blocks bounded by normal faults geomorphic analyses indicate a general southward trend of increasing tectonic uplift from region i into region ii where the highest frequency of mountain fronts with low values of s and ffd as well as rivers with the highest values of k occur over the crest of the subducted ridge field and historical seismic data for these regional trends include 1 fault scarps displacing late quaternary fluvial terraces and colluvial soils in areas of collisional responses 2 holocene latest pleistocene marine sediments uplifted tens of meters along normal faults in areas of isostatic response of region ii and 3 more frequent shallow high magnitude earthquakes in region ii this study indicates that spatial variations in the plate tectonic framework can be detected by regional morphometric analyses using techniques applied in extensional and compressional terranes of arid and semiarid regions but not previously applied to forearc systems along convergent plate boundaries in tropical areas

residence time indicators in groundwater the east midlands triassic sandstone aquifer the east midlands triassic sherwood sandstone aquifer which has been the subject of detailed radiometric age studies is used to investigate both inert and reactive constituents of groundwater as indicators of residence time detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data though without radiocarbon several inert indicators are defined including the isotopic ratios 18o 2h 36cl noble gas ratios as well as the halogen elements cl br f i and their element ratios these form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions except at outcrop where human impacts are also seen clearly the concentrations of cl mainly from atmospheric sources remain below 25 mg l 1 cl over a distance of some 30 km from outcrop reactive indicators the result of time dependent water rock interactions include 13c mg ca sr ca na cl and show diagnostic trends along the flow lines however the concentrations of certain trace elements li rb cs mn and mo which are not limited by solubility constraints show linear trends along the present day flow gradient this water rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the sherwood sandstone there is good correlation between some of the elements and 14c activities in the 1977 data set and this has been used to derive a concentration age relationship for the 1992 set of data a chemical timescale for the aquifer is then established using a li and b a combination of five trace elements the age of the fresh groundwater is thus shown to be up to 100 ka bp indicating the likelihood of semi continuous recharge during the devensian glacial period preceding the glacial maximum when no recharge occurred 10 20 ka bp this approach may be of value in extending groundwater dating beyond the radiocarbon timescale as well as interpreting sites where no radiocarbon data are available the scatter from the mean age line indicates those groundwaters which are derived from either rapid or slower than average flow zones within the aquifer as well as age stratification this stratification is borne out by a depth profile of groundwater from a new borehole near to outcrop which is shown by a combination of chemical and isotopic tracers to contain holocene overlying late pleistocene water

constraining the groundwater flow system and aquifer properties using major ions environmental traces and a simple physical model in china s jilantai basin this study uses major ions and environment isotopes 87sr 86sr 13c and 14c together with a proposed physical model to constrain hydrogeochemical processes groundwater ages recharge rates and physical parameters in china s jilantai basin the major processes are identified using major ions which include calcite dissolution and the exchange of na for ca in upstream areas and gypsum dissolution carbonate incongruent dissolution and silicate weathering in downstream areas sr and major ions indicate the dissolution of carbonate minerals or gypsum and silicate weathering 87sr 86sr variations indicate that shallow groundwater in discharge areas consists of more than 90 groundwater from rainfall in the ulan buh desert ubd and middle groundwater comes entirely from the helan mountains the major ions 87sr 86sr ratio and physical model reflect that inter aquifer mixing has occurred between shallow unconfined and upper confined aquifers but not in middle confined formations the 14c ages range from the present to 15 ka and the distribution of 14c residence times indicate that inter aquifer flow occurs on a regional scale and over the long term between shallow unconfined and upper confined aquifers the travel times using the physical model proposed in this paper are comparable to the 14c ages indicating that this model is suitable for calculating travel times for the middle confined aquifers that have effective aquitards the vertical leakage rates are 0 01 0 03 m day and the long term recharge rates are 15 mm year approximately 5 of annual rainfall the groundwater from this region is a locally valuable resource and the correct understanding of groundwater flow systems inter aquifer mixing and recharge rates is critical to managing these groundwater resources

geomorphic assessment of active tectonics in the acambay graben mexican volcanic belt spatial variations of quaternary deformation and tectonic activity of faults along the acambay graben are assessed using geomorphic and morphometric approaches the acambay graben is an east west trending structure of apparent quaternary age located in the central part of the mexican volcanic belt which gives rise to pronounced scarps over a distance of about 80 km continuing tectonic activity in the acambay graben is confirmed by recent well documented seismic episodes the intensity of active tectonics has been interpreted through a detailed geomorphic study of the fault generated mountain fronts and fluvial systems the combined geomorphic and morphometric data provide evidence for relative variations in tectonic activity among the acambay graben faults geomorphic indices suggest a relatively high degree of tectonic activity along the venta de bravo and the acambay tixmadeje faults followed in order of decreasing activity by the pastores temascalcingo and tepuxtepec faults spatial variations within faults have also been identified suggesting a higher level of tectonic activity at the tips of the faults this pattern of variation in the relative degree of tectonic activity is consistent with field evidence and seismic data for the acambay graben geomorphic evaluation of the acambay graben faults suggests that the acambay tixmadeje and venta de bravo faults and specifically the tips of these faults and a central segment near the town of venta de bravo should be considered as areas of potentially high earthquake risk 1998 john wiley sons ltd

understanding space time patterns of groundwater system by empirical orthogonal functions a case study in the choshui river alluvial fan taiwan summary natural or anthropogenic activities contribute to changes of groundwater levels in space and time understanding the major and significant driving forces to changes in space time patterns of groundwater levels is essential to groundwater management this study analyzes monthly observations of piezometric heads from 66 wells during 1997 2002 located in the choshui river alluvial fan of taiwan where groundwater has been the important local water resource for myriads of agricultural or industrial demands following spatiotemporal estimations of piezometric heads by bayesian maximum entropy method bme this work performs rotated empirical orthogonal function reof analysis to decompose the obtained space time heads into a set of spatially distributed empirical orthogonal functions eofs and their associated uncorrelated time series results show that the leading eofs represent the most significant driving forces to spatiotemporal changes of groundwater levels in the choshui river aquifer these include rainfall recharges from upstream choshui and pei kang river pumping activities from aquaculture usages in the coastal areas as well as water exchanges between surface and subsurface flow of choshui river in summary this study shows the strength of the reof analysis which can effectively provide integrative views of spatiotemporal changes of groundwater gaining insights of interactions between the groundwater system and other natural and human activities

high cesium concentrations in groundwater in the upper 1 2 km of fractured crystalline rock influence of groundwater origin and secondary minerals abstract dissolved and solid phase cesium cs was studied in the upper 1 2 km of a coastal granitoid fracture network on the baltic shield aspo hard rock laboratory and laxemar area se sweden there unusually high cs concentrations up to 5 6 g l 1 occur in the low temperature 1 median laxemar 3 7 g l 1 and groundwater with marine origin aspo hrl 4 2 g l 1 overall lower but variable cs concentrations were found in other types of groundwater the similar concentrations of cs in the saline groundwater which had a residence time in the order of millions of years and in the marine groundwater which had residence times in the order of years shows that duration of water rock interactions is not the single and primary control of dissolved cs in these systems the high cs concentrations in the saline groundwater is ascribed to long term weathering of minerals primarily cs enriched fracture coatings dominated by illite and mixed layer clays and possibly wall rock micaceous minerals the high cs concentrations in the groundwater of marine origin are in contrast explained by relatively fast cation exchange reactions as indicated by the field data and predicted by 1d solute transport modeling alkali cations with low energy hydration carried by intruding marine water are capable of nh 4 in particular and k to some extent replacing cs on frayed edge fes sites on illite in the fracture coatings the result is a rapid and persistent at least in the order of decades buildup of dissolved cs concentrations in fractures where marine water flows downward the identification of high cs concentrations in young groundwater of marine origin and the predicted capacity of nh 4 to displace cs from fracture solids are of particular relevance in the disposal of radioactive nuclear waste deep underground in crystalline rock

using groundwater geochemistry and environmental isotopes to assess the correction of 14c ages in a silicate dominated aquifer system summary the use of 14c to constrain groundwater residence times requires careful correction of 14c activities a14c and an assessment of the degree of inter aquifer mixing in groundwater of the campaspe valley in the southern murray basin australia 13c values of dissolved inorganic carbon dic range from 18 to 2 using these 13c values to correct 14c ages assuming that dissolution of or exchange with matrix calcite had occurred implies that locally 90 of the dic is derived from carbonates in turn this suggests that low salinity groundwater in the deeper confined calivil renmark formation up to 50 60 km from the basin margins in the campaspe valley has a component of modern recharge which would require that widespread leakage from the overlying shepparton formation had occurred however 87sr 86sr ratios and major ion geochemistry of groundwater imply that negligible inter aquifer mixing has occurred and that calcite dissolution is a very minor process the variable 13c values are most probably due to methanogenesis via reduction of co2 in the groundwater that results in the residual dic being enriched in 13c as methanogenesis by this mechanism has only a minor impact on a14c uncorrected 14c ages are a better estimate of groundwater residence times groundwater in the north of the campaspe valley has a residence time of 9 13 ka which agrees with ages calculated from head gradients and hydraulic conductivities calivil renmark groundwater from the adjacent pyramid hill region in an area where the aquifers contain lower hydraulic conductivity sediments is substantially older up to 20 25 ka the age of groundwater from the shepparton formation increases irregularly with depth with ages of in excess of 25 ka recorded at its base this study illustrates the need to fully understand hydrogeological processes in order to correct 14c ages especially in silicate dominated aquifers where dissolution of carbonates may not be the major process controlling 13c values

delineation of temporal variability and governing factors influencing the spatial variability of shallow groundwater chemistry in a tropical sedimentary island summary an attempt has been made to delineate the temporal variability and factors governing the shallow groundwater chemistry using analysis of variance anova and multivariate analysis notably r mode factor fa and hierarchical cluster analysis hca subsequently geostatistical isoplethic maps were applied to convey better understanding on the distribution of selected groundwater parameters the manukan island s shallow aquifer with sedimentary setting that constantly abstracted for freshwater supply has been selected for this study one way anova suggested that neither changes of tide level nor rainfall volume appeared to exert significant influence on the groundwater chemistry of the small island rather the groundwater chemistry was greatly governed by influence from seawater intrusion which characterized by considerable amount of ca na and cl such condition was well explained by a piper diagram where most plots were situated at the middle diamond shaped diagram indicating mixing condition fa likewise revealed that the shallow groundwater receives marked influence from carbonate dissolution and silicate weathering processes especially boreholes located in the inland area this can be clearly noted from the distinct groupings of relationships among different factors hca classified boreholes into three groups according to their locations in the coastal area suggesting significant chemical variations between boreholes with distance from coast such distribution pattern was particularly evident in the isoplethic map overall it appears that the shallow groundwater in the tropical island is not an appropriate source for drinking water in concern to its exceptionally high salinity and several elevated minor elements mn pb and se for this it is suggested that efforts in exploring other alternative sources should be performed outright

detrital and early diagenetic processes in late pleistocene and holocene sediments from the sw galicia bank inferred from high resolution enviromagnetic and geochemical records abstract u channel based high resolution magnetic and geochemical measurements supported by scanning electron microscopy x ray diffraction and fluorescence and grain size analyses of discrete samples were carried out on six sediment cores recovered from the sw flank of the galicia bank at the prestige s wreck area five magnetochemical facies reflecting the different sedimentary environments i e hemipelagic contouritic turbiditic sediment provenances and early diagenetic redoxomorphic processes i e mn peaks are defined on the basis of a cluster analysis the records showed climatically forced detrital signatures of regional importance associated with continental slope sedimentary processes the chronostratigraphy and correlation of the cores is based on 20 14 c ams dating recognition of heinrich like events h1 to h3 and well documented holocene climatic features from a geochemical and enviromagnetic perspective the late pleistocene to holocene evolution of the area shows two different sedimentation contexts mis 2 is dominated by down slope depositional processes the highest sedimentation rates 9 1 cm ky were achieved during this interval the major turbidite activity is recorded between 31 000 yr bp and 13 500 yr bp successive arrivals of ird h1 to h3 are also identified during this period in contrast holocene sedimentation was dominated by a mixture of pelagic hemipelagic and along slope depositional processes and presented considerable lower sedimentation rates 3 cm ky bottom currents intensification at 7000 yr bp and 4500 yr bp coinciding with late holocene warm events are also recognised during this stage

isotopic evidence for palaeowaters in the british isles before the 20th century groundwater circulation in the aquifers of the british isles had largely adjusted to the temperate maritime climate and sea levels established over the past 10 ka since the end of the pleistocene however in the last 100 a this natural regime has been disturbed by abstraction of water for public supply and industrial use and palaeowaters from earlier recharge episodes are now becoming a factor to be considered in water balance estimates this paper presents a synthesis of the existing palaeowater distribution in the british isles based on isotopic evidence 18o 2h and and14c as such it has relevance to palaeoclimatic studies in addition to the water resource implications the triassic basins of england and northern ireland contain saline waters beyond the range14c dating 40 ka stable isotopic ratios show enrichment in some basins and depletion in others without an overall pattern that would explain all the observed compositions the results for the wessex basin suggest recharge in pre quaternary times but for the other basins some flushing by pleistocene or holocene meteoric waters is indicated isolated occurrences of apparently long residence waters are found elsewhere throughout the british isles for example from carboniferous and lower palaeozoic strata in such cases environmental isotopes are more useful as constraints on hydrogeological models than as indicators of palaeoconditions major water supply aquifers are restricted almost entirely to england the two sandstone formations triassic sherwood sandstone and cretaceous lower greensand have a greater range of stable isotopic values between phreatic and confined conditions than the two carbonate formations jurassic lincolnshire limestone and cretaceous chalk this indicates that the sandstone aquifers are better archives of information on palaeoconditions than the carbonate aquifers they show that atmospheric circulation patterns over britain have probably remained the same since the late pleistocene however 14c data from all four of the major aquifers emphasise the hiatus in recharge during periglacial conditions which occurred between the late pleistocene and early holocene

reversal records in marine marls and delayed acquisition of remanent magnetization records of geomagnetic reversals frozen into the magnetic components of sediments provide a means to study the time dependent behaviour of the geomagnetic field during polarity transitions although sedimentary records have the advantage of being readily available and continuous the process by which they acquire a remanent magnetization is still not fully understood1 magnetites which lose their magnetization at relatively high temperatures 580 c are generally considered to carry the primary remanence of the sediment that is to record the palaeomagnetic direction here we describe two reversed to normal transitional records from marine marls in which this high temperature component shows a delayed remanence acquisition relative to a lower temperature component in these samples therefore the high temperature component does not reflect geo magnetic changes during the reversal at least for marine marls detailed palaeomagnetic rock magnetic and geochemical studies are apparently necessary to judge the validity of reversal records

discharge of hydrothermal fluids through sediment at the escanaba trough gorda ridge odp leg 169 assessing the effects on the rock magnetic signal an integrated rock magnetic and multivariate statistical analysis of a suite of sediment samples recovered from odp sites 1037 and 1038 leg 169 escanaba trough gorda ridge spreading center ne pacific ocean has been carried out to assess the use of the sediment magnetic signal as a tracer of post depositional alteration related to the discharge of hydrothermal fluids through these sediments the uppermost above 40 mbsf section of three separate holes holes 1037 b 1038 i and 1038 g was sampled previous sedimentological and geochemical studies indicated that these holes represent a transect from unaltered to strongly hydrothermally influenced sediments analysis of nrm arm anisotropy of magnetic susceptibility ams hysteresis parameters and low temperature magnetic properties suggest increasing alteration of the magnetic minerals with increasing circulation of hydrothermal circulation of fluids fuzzy c means clustering combined with non linear mapping yields a more elaborate picture because similar alteration groupings at different holes can be compared at hole 1037 b a sedimentary reference site drilled away from the area of high heat flow the rock magnetic signal is a sensitive record of changes in detrital inputs magnetite and some monoclinic pyrrhotite are detected the detrital magnetic signal is still apparent at intermediate hole 1038 i but cluster analysis detects an increasing hydrothermal influence on the magnetomineralogy in the lower part of the hole strong hydrothermal alteration at hole 1038 g results in a complete loss of the detrital diagenetic magnetic signal which is replaced by a much weaker hydrothermal signal composed of monoclinic pyrrhotite and pyrite the alteration of the magnetic signal is not restricted to the uppermost few meters of the sediment column and the magnetic properties of the sediment can be used to trace even minor alterations of marine sediments related to the lateral and vertical advection of hydrothermal fluids which may easily be overlooked by more traditional methods fl 2000 elsevier science b v all rights reserved

using 3h and 14c to constrain the degree of closed system dissolution of calcite in groundwater abstract this study uses 3h concentrations 14c activities a14c 87sr 86sr ratios and 13c values to constrain calcite dissolution in groundwater from the ovens catchment se australia taken in isolation the 13c values of dissolved organic c dic and 87sr 86sr ratios in the ovens groundwater imply that there has been significant calcite dissolution however the covariance of 3h and 14c and the calculated initial 14c activities a014c imply that most groundwater cannot have dissolved more than 20 of 14c free calcite under closed system conditions rather calcite dissolution must have been partially an open system process allowing 13c and 14c to re equilibrate with co2 in the unsaturated zone recognising that open system calcite dissolution has occurred is important for dating deeper groundwater that is removed from its recharge area in this and other basins the study is one of the first to use 14c and 3h to constrain the degree of calcite dissolution and illustrates that it is a valuable tool for assessing geochemical processes in recharge areas

active tectonics landscape evolution and sediment dynamics in dehra dun northwest himalaya inferred from geomorphic indices and gis tools abstract geomorphic evolution of the frontal parts of active mountain belts is strongly influenced by tectonic processes usually manifested in fluvial structural and morphotectonic parameters of the landscape geomorphic indices have long been used for understanding the tectonic imprints in river basins however their applicability and validation from field observations in the himalayan basins have often been debated here we test the applicability of several geomorphic indices in the western dehra dun intermontane valley that includes well known tectonic elements such as main boundary thrust mbt main frontal thrust mft santaurgarh thrust st and other smaller faults based on the spatial distribution of the values of different geomorphic indices we map four different tectonic zones to represent the relative tectonic activity from low to very high we conclude from morphometric analysis that the mbt and the st are active faults however we do not find any geomorphic evidence of recent activity along several other faults mapped in this region or any deformation in the major fan units we argue that active tectonics has not played a significant role in shaping the landforms in this region except for providing accommodation space and sediment supply for the deposition of fan units we have further employed dem and limited borehole data to understand the sediment storage and excavation at late late quaternary time scale we compute the average stored volume of sediments since 50 ka as 8 03 1010 m3 using borehole data and 12 24 1010 m3 gis approach total eroded volume has been computed as 0 47 1010 m3 using borehole data and 0 64 1010 m3 gis approach these volumes give a time averaged sediment discharge leaving the dun as 0 21 0 39 106 m3 yr over late quaternary period we note that the estimated average eroded material during the incision phase is only 5 6 of the total accumulated sediment volume further the average estimated volume 8 03 12 24 1010 m3 in the valley is nearly half of the volume of the sediment that can be accommodated 27 2 1010 m3 in the valley also the present day sediment supply to the dun 0 14 106 m3 yr is low in comparison to estimated average erosion rate our results therefore suggest that the valley is only half filled and is in excavation phase since late quaternary mostly driven by climatic perturbations

flow pattern and residence time of groundwater within the south eastern taoudeni sedimentary basin burkina faso mali the knowledge about groundwater flow conditions within the southeastern taoudeni basin aquifer shared by burkina faso and mali is relatively limited with very little information on potentiometric heads recharge processes residence time and water quality a better evaluation of groundwater resources in this area is a strategic point for water resources management in the entire soudano sahelian region which endures since the beginning of the twentieth century a continuous decrease in precipitation amount this paper provides a transboundary synthesis using water 18o 2h and 3h and carbon isotopes 13c and 14c in conjunction with hydrogeological and hydrochemical data the objectives are to improve the conceptual model of groundwater recharge and flow within this sandstone reservoir and to assess the changes in the aquifer due to water abstraction and recent climate changes including an insight into sahelian aquifers palaeorecharge processes the local meteoric water line for the bobo dioulasso station is proposed 2h 8 0 0 5 18o 10 2 2 1 two main tendencies can be derived from groundwater chemistry first a slight evolution from the ca mg hco3 type towards a na k hco3 type that indicates developed interactions between groundwater and clay minerals related to the residence time of groundwater a second tendency towards cl no3 so4 hco3 water types indicates the anthropogenic influence on groundwater related to the poor sanitary conditions observed around wells the carbon 14 activity measured on the tdic varies between 0 3 and 122 pmc so our record contains samples covering a wide period from actual to pleistocene suggesting a continuous recharge of the system through time even if the sahel region has endured many different climate phases which have influenced the infiltration and recharge processes all groundwater samples have stable isotope compositions in the range of the present day regional and global meteoric water line which suggests that the sampled groundwater was not significantly affected by evaporation during recharge evolved waters are depleted relative to unevolved samples by 1 5 2 in 18o and 10 15 in 2h the whole dataset support the hypothesis of a largely unified homogeneous aquifer system with a multilayered structure but it also points out the very low renewability of the resource and a strong anthropogenic contamination of the shallowest horizons

late quaternary tectonic landforms and fluvial aggradation in the saryu river valley central kumaun himalaya abstract the present study has been carried out with special emphasis on the aggradational landforms to explain the spatial and temporal variability in phases of aggradation incision in response to tectonic activity during the late quaternary in the saryu river valley in central kumaun himalaya the valley has preserved cut and fill terraces with thick alluvial cover debris flow terraces and bedrock strath terraces that provide signatures of tectonic activity and climate morphostratigraphy of the terraces reveals that the oldest landforms preserved south of the main central thrust the fluvial modified debris flow terraces were developed between 30 and 45 ka the major phase of valley fill is dated between 14 and 22 ka the youngest phase of aggradation is dated at early and mid holocene 9 3 ka following this several phases of accelerated incision erosion owing to an increase in uplift rate occurred as evident from the strath terraces seven major phases of bedrock incision uplift have been estimated during 44 ka 3 34 mm year 35 ka 1 84 mm year 15 ka 0 91 mm year 14 ka 0 83 mm year 9 ka 1 75 mm year 7 ka 5 38 mm year and around 3 ka 4 4 mm year from the strath terraces near major thrusts we postulate that between 9 and 3 ka the terrain witnessed relatively enhanced surface uplift 2 5 mm year

residence time of chalk groundwaters in the paris basin and the north german basin a geochemical approach the comparative geochemical and isotopic study of confined and unconfined chalk groundwaters of the paris basin and the n german basin proves a significant chemical evolution during groundwater flow from the recharge zones to the deep confined aquifer different time dependent geochemical parameters have been tested as dating tools cation ratios sr2 ca2 mg2 ca2 n no 3 noble gas contents as paleotemperature indicators ne ar kr xe radiogenic he 13c 14c 18o 2h 3h cation ratios and 13c show the importance of incongruent dissolution processes in the chalk aquifer water rock interactions were taken into account in a multi step dissolution model to determine radiocarbon groundwater ages the oldest waters in the confined part of the paris basin chalk with maximum 14c ages of 14 000 a b p contain pleistocene recharge components as can be shown by a stable isotope depletion and noble gas temperatures significantly lower than in recent groundwaters chalk waters at the lagerdorf site in northern germany show a distinct stratification with respect to residence times and hydrochemistry

diagenetic alterations related to marine transgression and regression in fluvial and shallow marine sandstones of the triassic buntsandstein and keuper sequence the paris basin france abstract the distribution of diagenetic alterations in triassic fluvio deltaic quartzarenitic to sublitharenitic lowstand systems tract lst sandstones of the gres a voltzia formation anastomosing fluvial quartzarenitic transgressive systems tract tst sandstones of the gres a roseaux formation and shallow marine quartzarenitic to sublitharenitic tst sandstones of the gres coquiller formation the paris basin france can be linked to transgression and regression events and thus to the sequence stratigraphic context near surface eogenetic alterations which display a fairly systematic link to the depositional facies and sequence stratigraphic framework include i cementation by meteoric water calcite 18 o 8 9 and 13 c 9 1 in the fluvio deltaic lst sandstones ii cementation by mixed marine meteoric calcite 18 o 5 3 to 2 6 and 13 c 3 9 to 1 3 and dolomite 18 o 4 6 to 2 6 and 13 c 2 9 to 2 3 in the foreshore tst sandstones and below parasequence boundaries pb and transgressive surface ts and in the shoreface tst sandstones below maximum flooding surfaces mfs being facilitated by the presence of carbonate bioclasts iii dissolution of detrital silicates and precipitation of k feldspar overgrowths and kaolinite particularly in the fluvio deltaic lst sandstones owing to effective meteoric water circulation and vi formation of autochthonous glauconite which is increases in abundance towards the top of the fluvio deltaic lst sandstones and along ts and in the shoreface tst sandstones by alteration of micas owing to the flux of seawaters into the sandstones during transgression whereas parautochthonous glauconite is restricted to the ts sandstones owing to marine reworking mesogenetic alterations which include cementation by quartz overgrowths and illite display fairly systematic link to fluvio deltaic lst sandstones this study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

cyclostratigraphy and rock magnetic investigation of the nrm signal in late miocene palustrine alluvial deposits of the librilla section se spain 1 we constructed a high resolution time frame for the cyclic continental palustrine alluvial section of librilla se spain which covers the onset of the messinian salinity crisis in the marine realm the section was dated earlier by garces et al 1998 using magnetostratigraphy we resampled part of the section that contained a reversed overprint in detail to refine the magnetostratigraphy and to investigate the behavior of the natural remanent magnetization nrm signal the detailed sampling yielded a better constrained position of the upper reversal of chron c3an 1n by counting the number of cycles in c3an 1n and taking into account the duration of this chron we were able to show that the basic sedimentary cycles in librilla reflect climatic precession subsequently the sedimentary pattern was tuned to the summer insolation curve providing a high resolution time two intervals of complex nrm behavior were identified showing normal and reversed overprints the reversed overprints seemed to be restricted mainly to gray palustrine layers the analysis of coercivity components revealed no difference between samples with overprints or real nrm directions we performed fuzzy c means cluster analysis on a geochemical data set to link magnetic behavior to geochemical proxies resulting in a three cluster model that roughly describes lithology remarkably all the samples with a normal overprint belong to one particular cluster the reversed overprints however do not show any relation to the cluster partition we favor the explanation of garces et al 1998 that the reversed overprint would be related to the messinian salinity crisis

the groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks an application of natural environmental tracers isotope data of precipitation and groundwater in parts of the voltaian basin in northern ghana were used to explain the groundwater recharge regime in the area groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area it is therefore important to establish the processes and sources of groundwater recharge 18o and 2h data for local precipitation suggest enrichment relative to the global meteoric water line gmwl and indicate that precipitation takes place at a relative humidity less than 100 the groundwater data plot on an evaporation line with a slope of 5 suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone this finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates groundwater recharge estimates from the chloride mass balance cmb method suggest recharge in the range of 1 8 32 of the annual average precipitation in the form of rainfall the highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area in the northern parts of the study area groundwater recharge is lower than 12 the recharge so computed through the application of the cmb methodology takes on a spatial distribution akin to the converse of the spatial pattern of both 18o and 2h in the area as such the locations of the highest recharge are associated with the most depleted values of the two isotopes this observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water the percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates at the same time the amount of water that finally reaches the water table is considerably reduced copyright 2013 john wiley sons ltd

historic large earthquake induced soft sediment deformation features in the sub himalayan doon valley well preserved soft sediment deformation structures were observed at six sites along the course of the baldi nadi in the doon valley of the garhwal himalaya these deformed structures lie in mid and side channel bars of the braided baldi stream the deformed sediments are composed of unconsolidated alternations of mud silt and very fine sand with ripple lamination deformation is restricted to a single stratigraphic layer bounded by undeformed beds suggesting synsedimentary deformation these features can be traced laterally along the course of the braided baldi nadi over a distance of 7 km in isolated bar deposits at one stratigraphic level 1 5 2 m above the lean season water level the deformed features display over steepening of sedimentary strata folding graben type faulting plume like intrusion flame structure slumping related to disrupted bedding and pear drop structure the style and type of deformation vary considerably in the different segments within a single bed while the intensity may be same at one site the deformation features of the baldi nadi are interpreted to be the product of liquefaction and fluidization of unconsolidated mud and silt during historic earthquake s related to the past seismic activity of the main boundary thrust mbt and the himalayan frontal fault hff or blind thrust the intensity of deformation provides an opportunity to reconstruct the felt area magnitude of large historic earthquake s and helps in tracing the palaeoearthquake epicentre the observed earthquake induced soft sediment deformation features indicate that in addition to the 1905 great earthquake the doon valley was also affected by historic earthquake s of magnitude similar 7 possibly corresponding to those of 1803 and or 1720 if not older

constraining groundwater flow residence times inter aquifer mixing and aquifer properties using environmental isotopes in the southeast murray basin australia environmental isotopes particularly d 18 o d 2 h and d 13 c values 87 sr 86 sr ratios and a 14 c constrain geochemical processes recharge distribution and rates and inter aquifer mixing in the riverine province of the southern murray basin due to methanogenesis and the variable d 13 c values of matrix calcite d 13 c

matrix porosity as the most important parameter of fissured rocks for solute transport at large scales simple considerations show that tracer and or pollutant velocity at large scales in fissured rocks can be described by the formula vtnp h x k where vt is the mean velocity of a conservative tracer or pollutant np is the matrix porosity h x is the hydraulic gradient and k is the hydraulic conductivity the applicability of the formula is discussed and its validity tested in several case studies in which hydraulic conductivities calculated from either pollutant transport velocity or environmental tracer ages were compared with those known or estimated from other determinations the influence of matrix diffusion on the environmental tracer ages can also be proved independently by comparison of the rock volume vrock estimated from the hydrogeologic map with that calculated from volumetric flow rate q age of tracer tt and matrix porosity vrock qttnp

origins of streamflow in a crystalline basement catchment in a sub humid sudanian zone the donga basin benin west africa inter annual variability of water budget during the last quarter of the 20th century west africa underwent a particularly intense and generalized drought during this period the biggest drops in streamflow were observed in the sudanian zone rather than in the sahelian zone but the reasons are still poorly understood in 2000 a meso scale hydrological observatory was set up in the sub humid sudanian zone of the upper oueme valley benin three embedded catchments of 12 586 km2 located on a crystalline bedrock were intensively instrumented to document the different terms of the water budget and to identify the main streamflow generating processes and base flow mechanisms at different scales geophysical hydrological and geochemical data were collected throughout the catchments from 2002 to 2006 crossing these data helped define their hydrological functioning the region has seasonal streamflow and the permanent groundwater in the weathered mantle does not drain to rivers instead seasonal perched groundwaters are the major contributor to annual streamflow the perched groundwaters are mainly located in seasonally waterlogged sandy layers in the headwater bottom lands called bas fonds in french speaking west africa of 1st order streams during the period 2003 2006 regolith groundwater recharge ranged between 10 and 15 of the annual rainfall depth depletion of permanent groundwater during the dry season is probably explained by local evapotranspiration which was seen not to be limited to gallery forests during the 4 year study period a reduction of 20 in annual rainfall led to a 50 reduction in streamflow this reduction was observed in the two components of the flow direct runoff and drainage of perched groundwater thanks to the comprehensive dataset obtained the results obtained for the donga experimental catchment are now being extrapolated to the whole upper oueme valley which can be considered as representative of sub humid sudanian rivers flowing on a crystalline basement for example the upper courses of several major west african rivers senegal niger bani and volta

analysis of drainage basin symmetry as a rapid technique to identify areas of possible quaternary tilt block tectonics an example from the mississippi embayment there is a coincidence of seismicity and major river valleys in the southwestern mississippi embayment that suggests control of the drainage pattern by northwest trending faults pleistocene river terraces reveal a strong southwestward preferred river migration in this region that may be a result of fault block tilting a rapid new technique of drainage basin analysis is herein presented that quantifies transverse topographic basin symmetry these data permit discrimination of random stream migrations and regionally preferred stream migrations and identify the direction of maximum migration if bedrock dip can be shown to be a negligible influence on stream migration then the direction of regionally preferred migration implies a period of ground tilting in that direction drainage basin asymmetry vectors bearing and degree of asymmetry calculated from transverse topographic profiles of 271 4 km basin segments in the study area suggest preferred stream migration in response to west southwest ward ground tilting bearing 259 the eastward regional dip of bed rock horizons only locally influences migration river terrace distributions reveal a chronology of stream migration episodes southwestward migration in the ouachita saline and arkansas river basins occurred during early to middle pleistocene time in the southwestern mississippi embayment a wisconsin early holocene southwestward migration episode is evidenced along southeast flowing reaches of the ouachita and arkansas rivers but not along the southeast flowing reach of the intervening saline river suggesting that these rivers overlie separate northwest trending tilt blocks although this technique does not provide direct evidence of ground tilting it provides a quick look method of identifying possible tilting elements in neotectonic regions using only topographic maps this technique is of greatest utility where active faults are concealed or poorly exposed such as in the mississippi embayment

hydrochemical and isotopic characteristics of groundwater in the ndop plain northwest cameroon resilience to seasonal climatic changes shallow groundwater 30 mbgl is an essential source of drinking water to rural communities in the ndop plain northwest cameroon as a contribution to water management the effect of seasonal variation on the groundwater chemistry hydrochemical controls drinking quality and recharge were investigated during the peaks of the dry january and rainy september seasons field measurements of physical parameters were preceded by sampling 58 groundwater samples during both seasons for major ions and stable isotope analyses the groundwater which was barely acidic mean ph of 6 and less mineralised tds ca2 mg2 k and na mg2 ca2 k in the dry and rainy seasons respectively but that of anions text hco 3 text no 3 cl text so 4 2 f was similar in both seasons this suggests a negligible effect of seasonal variations on groundwater chemistry the groundwater which was camghco3 and nahco3 is chemically evolved rainfall camgso4cl in the area silicate mineral dissolution and cation exchange were the main controls on groundwater chemistry while there was little anthropogenic influence the major ions and tds concentrations classified the water as suitable for human consumption as per who guidelines the narrow cluster of 18o and d of same groundwater from both seasons between the 18o and d values of may june precipitation along the ndop meteoric water line indicates meteoric origin rapid recharge after precipitation and timing of recharge between may and june rainfall diffuse groundwater recharge mainly occurs at low altitudes 1 400 m asl within the plain besides major ions and tds the similar 18o and d of groundwater from both seasons indicate a consistent groundwater recharge and flow pattern throughout the year and resilience to present day short term seasonal climatic variations however controlled groundwater abstraction is recommended given the increasing demand

the hydrogeology and groundwater resources development of the cambro ordovician sandstone aquifer in saudi arabia and jordan abstract the saq cambro ordovician sandstones form the major national aquifer in saudi arabia and jordan significant abstraction of groundwater has taken place since the early 1950s and monitoring of the aquifer responses indicates a moderate transmissivity but high specific yield the groundwater quality is excellent for irrigation which is the present major use and is also good for potable purposes although large drawdowns are being experienced locally in confined areas of the aquifer the unconfined area responses show the aquifer to have an excellent potential for development under groundwater mining principles that may be considered for use outside the areas of occurrence

reconsidering himalayan river anticlines the observation that major himalayan rivers flow parallel to and down the axis of anticlines oriented transverse to the primary structural grain of the range has puzzled geomorphologists for decades although there is a general consensus that the courses of trans himalayan rivers predate the himalayan orogeny the close association of rivers and structural highs would not be expected to result from the superposition of rivers onto pre existing structures moreover in the past several decades structural studies have shown that the development of river anticlines represents the most recent phase of deformation in the range it is proposed that himalayan river anticlines are the consequence of focused rock uplift in response to significant differences between net erosion along major rivers and surrounding regions this hypothesis is supported by large gradients in observed and predicted erosion rates across major himalayan rivers and by results from an isostasy driven model which requires relatively low flexural rigidities to match the wavelength of himalayan river anticlines whether the amplitude of these structures is due to isostasy or also reflects active crustal channeling is not well constrained but given the uncertainty in the flexural rigidity and in the local and far field erosion rates both possibilities remain viable explanations given the observed correlation between the arun river anticline and local rainfall maxima it is proposed that himalayan river anticlines are the expression of a relatively fine scale linkage between tectonics erosion and climate superimposed on the broader and older canvas of the himalayan orogeny finally it is suggested that the development of river anticlines represents one example along a continuum of features arising from different degrees of erosion structure coupling in active orogens

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

geochemical evidence for efficient aquifer isolation over geological timeframes aquitards layers of rock having low permeability have been suggested as potential long term reservoirs for toxic materials such as nuclear or chemical waste but information about the isolation properties of aquitard layers is essential to evaluate whether they can indeed be used safely as reservoirs here we investigate the long term mobility of groundwaters between two aquifers surrounding an aquitard layer in the eastern recharge area of the paris basin france using helium isotopes as a geochemical tracer the deeper trias sandstone aquifer which lies above the crystalline basement accumulates radiogenic 4he and primordial 3he from large regions of the crust and mantle at rates comparable to the degassing of the whole crust1 and of mid ocean ridges2 we show that the overlying carbonate dogger aquifer which is separated from the trias aquifer by an aquitard layer consisting of a 600 m succession of shales and clays is stagnant and has been extremely well isolated from the trias over the past several million years this finding together with previous studies at the centre of the paris basin3 4 shows that diffusive mass transfer across aquitards is negligible and that cross formational flow in basins takes place preferentially in faulted areas

establishing constraints on groundwater ages with 36cl 14c 3h and noble gases a case study in the eastern paris basin france abstract groundwaters from the tithonian kimmeridgian oxfordian and upper dogger aquifers within the eastern part of the paris basin france were characterised using 3 h 14 c and 36 cl and noble gases tracers to evaluate their residence times and determine their recharge period this information is an important prerequisite to evaluating the confinement properties of the callovo oxfordian clay formation sandwiched between the oxfordian aquifer and the dogger aquifer currently being investigated by the french nuclear waste management agency andra for radioactive waste disposal data presented in this paper are used to test 4 hypotheses 1 the oxfordian limestone is isolated from the overlying tithonian kimmeridgian surface aquifer this first hypothesis is supported by the presence of measurable 3 h activities in groundwaters from the surface aquifer 6 11 tu and by its absence in groundwaters derived from deeper aquifers 2 the callovo oxfordian clay sequence in the vicinity of the url serves as an effective barrier to advective flow and transport between the underlying upper dogger aquifer and the overlying oxfordian limestone aquifer this second hypothesis is supported by relatively low concentrations of cl 3 5 78 mg l 1 na 15 145 mg l 1 br 0 08 0 4 mg l 1 and 4 he rad 0 2 2 3 ccstp g 1 and slightly higher 36 cl cl ratios 2 7 59 10 15 at at 1 in groundwaters from the oxfordian aquifer compared to those from the upper dogger aquifer 345 4027 mgcl l 1 402 2390 mgna l 1 1 8 22 2 mgbr l 1 1 6 37 2 ccstp he g 1 1 5 10 15 at 36 cl at 1 cl 3 groundwaters from the oxfordian aquifer in the vicinity of url are pre holocene with residence times exceeding 10 ka geochemical and isotopic lines of evidence for this hypothesis include a 13 c values measured on oxfordian aquifer waters that are close to 13 c of the aquifer matrix reflecting strong isotopic exchange over several thousand years b noble gas temperatures that indicate recharge temperatures between 3 and 8 6 c lower by 2 7 c than the modern average temperature in this area c radiogenic 4 he concentrations between 0 16 10 5 and 2 3 10 5 ccstp g 1 of water about 2 3 orders of magnitude greater than the 4 he concentration of air equilibrated water 4 groundwater residence time for the upper dogger aquifer in the vicinity of the url probably exceed several hundred thousand years such long residence times are indicated by the accumulation of radiogenic he up to 37 10 5 ccstp g 1 assuming a closed system primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of well defined 36 cl cl input ratio knowledge about the 4 he rad sources for oxfordian and dogger aquifers knowledge about transport processes occurring through the dogger aquifer and the extensive dilution of initial 14 c activities by dissolution exchange with aquifer matrix overall however although the data presented in this paper remain semi quantitative due to inevitable intrinsic limitations of the methods none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the url

groundwater residence time and palaeohydrology in the otway basin south australia 2h 18o and 14c data stable isotopes 2h 18o and 13c and radiocarbon 14c have been used in conjunction with chemical data to evaluate recharge mechanisms groundwater residence time and palaeohydrology within the confined dilwyn sand aquifer in the gambier embayment of the otway basin this aquifer does not receive recharge down gradient of the hydraulic hinge line and data have been interpreted along two discrete flow lines the mean residence time of groundwater determined by 14c in the confined aquifer from the hydraulic hinge position to the sea a distance of about 50 km along an inferred flow path is approximately 12 800 years the corresponding hydraulic travel time calculated from darcy s law is approximately 49 000 years the apparent discrepancy may be a result of eustatic sea level lowering during the last glacial because the groundwater system is hydraulically connected to the sea lower sea level would result in increased gradients and a decrease in groundwater residence time variations in stable isotopic composition along flow lines suggest a number of recharge mechanisms stable isotope data indicate progressive depletion of 2h and 18o in the groundwaters over the past 30 000 years groundwaters older than about 10 000 years b p were recharged either during a cooler climate climatic regime lower precipitation evapotranspiration and temperature and or the vapour source s had travelled over greater continental mass than those recharged over the past 10 000 years lower chloride concentrations in some of the older groundwaters indicate lower evapotranspiration rates in the recharge areas before 10 000 years ago

origin of the shallow groundwater system in the southern voltaian sedimentary basin of ghana an isotopic approach the development and management of groundwater resources require an ability to understand and identify the recharge source to the groundwater system stable and radioactive isotope data have been used to investigate the source of recharge and the age of the shallow groundwater system within the southern voltaian sedimentary basin svsb of ghana as part of an on going groundwater development project the tritium concentrations in the groundwater samples are very low and range from less than 1 7 2 t u while measured 14c content ranges from 43 to 108 modern carbon the tritium concentration of rainfall ranges from less than 1 4 t u the 18o values of groundwater samples range from 4 2 to 2 6 while the d values range from 21 to 10 stable isotopic data of the groundwater samples lie either on or close to the global meteoric water line gmwl on the d 18o plot and indicate that the shallow groundwater in the area is derived from meteoric water that has undergone no significant degree of kinetic evaporation during recharge no indication of paleo recharge can be inferred from the 18o and 2h composition of the groundwater current tritium concentration in the groundwater is generally low however it proved useful in the qualitative identification of modern recharge radiocarbon deduced ages range from about b p to modern and indicate young recharge to the shallow groundwater system

earthquake recurrence and rupture dynamics of himalayan frontal thrust india the black mango fault is a structural discontinuity that transforms motion between two segments of the active himalayan frontal thrust hft in northwestern india the black mango fault displays evidence of two large surface rupture earthquakes during the past 650 years subsequent to 1294 a d and 1423 a d and possibly another rupture at about 260 a d displacement during the last two earthquakes was at minimum 4 6 meters and 2 4 to 4 0 meters respectively and possibly larger for the 260 a d event abandoned terraces of the adjacent markanda river record uplift due to slip on the underlying hft of 4 8 0 9 millimeters per year or greater since the mid holocene the uplift rate is equivalent to rates of fault slip and crustal shortening of 9 6 3 5 7 0 millimeters per year and 8 4 3 6 7 3 millimeters per year respectively when it is assumed that the hft dips 30 10

foreland sedimentation in himalayan tectonic regime a relook at the orogenic process by raiverman v 2002 bishen singh mahendra pal singh publishers 23 a connaught place p o box 137 dehradun 248 001 india 378 pp price us 125

pattern of active tectonic deformation across the churachandpur mao thrust zone of manipur hills indo myanmar range ne india inferences from geomorphic features and indices abstract the churachandpur mao thrust cmt in indo myanmar range imr is known to be tectonically active but nevertheless the extent and pattern of activities on it and effects thereof on the surrounding region has not been determined as yet we herein present the results of our tectonic geomorphological investigations on these aspects across a long stretch of cmt zone spanning western imphal intermontane valley and enclosing frontal mountains the nne ssw trending cmt and nw se trending sekmai fault have subdivided the area into four tectonic blocks geomorphic features in conjunction with statistically analyzed mountain front sinuosity index smf stream length gradient index sl hypsometric integral hi drainage basin asymmetry factor af and transverse topography symmetry factor t reveal variations in nature and extent of tectonic activities and thus the pattern of surface deformation in these tectonic blocks tectonic blocks to the north of sekmai fault are experiencing more intense activities than the tectonic blocks to the south of sekmai fault north of the sekmai fault the cmt s footwall is experiencing the most intense activity and thus severe surface deformation in the area whereas the tectonic activity in the cmt s hanging wall here is only intense in the northern part to the south of sekmai fault while the hanging wall of the cmt is experiencing relatively moderate tectonic activities the footwall of the cmt is experiencing moderate to intense tectonic activities in different parts being most intense close to the sekmai fault tectonic activities have caused an overall southward down tilting of the cmt s footwall to the north of sekmai fault and overall northward down tilting of the remaining three tectonic blocks evidently the tectonic activities and thus the pattern of active surface deformation in the cmt zone of the area is significantly influenced by the transverse sekmai fault

diagenetic pyritisation under eastern mediterranean sapropels caused by downward sulphide diffusion recurrent organic rich layers sapropels in eastern mediterranean sediments are enriched in corg fe and s sulphur and fe are enriched in a zone immediately below the sapropels whereas corg is not 34s values of bulk sediments and simple mass balance calculations indicate that so42 reduction has taken place in an open system with all hs formed at or close to the sediment surface formation of pyrite in the sapropel was fe limited and consequently excess hs was able to migrate downwards downward sulphidisation this resulted in the formation of pyrite below the sapropel by reaction of this hs with solid phase ferric iron and fe2 diffusing upwards from underlying sediments the fe2 source probably includes fe hydr oxide layers formed at former oxidation fronts above previously deposited and buried sapropels this downward sulphidisation mechanism allows accumulation of twice as much s in alternating organic rich anoxic organic poor suboxic sediments compared to what is preserved in organic rich anoxic sediments

drainage response to active tectonics and evolution of tectonic geomorphology across the himalayan frontal thrust kumaun himalaya abstract we present the results of integrated studies of geomorphic indices of drainage networks and landforms developed across the mountain front along the himalayan frontal thrust hft between the dabka and baur rivers kumaun himalaya the hft is a morphogenic structure in nature creating a 100 m high e w trending escarpment that extends 21 km geomorphological evidence indicates 10 5 km westward migration of the dabka river and 5 2 km eastward migration of the baur river these migrations are a result of uplift of the hanging wall along the hft the hft is offset by a transverse fault which suggests that the latter postdates the reactivation of the hft between 500 and 100 ka presence of different levels of strath terraces along the mountain front suggests the active nature of the hft to assess the relative tectonic activity morphometric indices such as stream gradient sl index mountain front sinuosity s mf index and ratio of valley floor width to valley height vf have been analyzed results of the former two are consistent with the tectonic landforms developed in thrust zones paleochannels of the dabka and baur rivers are characterized by high vf values while other valleys show low vf values quaternary alluvial sediments have been deformed along the pawalgarth thrust a splay of the hft deformation has resulted in the formation of the pawalgarh anticline a thrust related asymmetric fold

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

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

14c age reassessment of groundwater from the discharge zone due to cross flow mixing in the deep confined aquifer abstract in a groundwater flow system the age of groundwater should gradually increase from the recharge zone to the discharge zone within the same streamline however it is occasionally observed that the groundwater age becomes younger in the discharge zone in the piedmont alluvial plain and the oldest age often appears in the middle of the plain a new set of groundwater chemistry and isotopes was employed to reassess the groundwater 14c ages from the discharge zone in the north china plain ncp carbonate precipitation organic matter oxidation and cross flow mixing in the groundwater from the recharge zone to the discharge zone are recognized according to the corresponding changes of hco3 or dic and 13c in the same streamline of the third aquifer of the ncp the effects of carbonate precipitation and organic matter oxidation are calibrated with a 13c mixing model and dic correction but these corrected 14c ages seem unreasonable because they grow younger from the middle plain to the discharge zone in the ncp the relationship of cl content and the recharge distance is used to estimate the expected cl content in the discharge zone and ln a14c cl is proposed to correct the a14c in groundwater for the effect of cross flow mixing the 14c ages were reassessed with the corrected a14c due to the cross flow mixing varying from 1 25 to 30 58 ka and the groundwater becomes older gradually from the recharge zone to the discharge zone the results suggest that the reassessed 14c ages are more reasonable for the groundwater from the discharge zone due to cross flow mixing

a paleomagnetic and geochemical record of the upper cochiti reversal and two subsequent precessional cycles from southern sicily italy abstract a detailed paleomagnetic and geochemical study of the upper cochiti n r reversal recorded in marine marls on southern sicily shows two consecutive and very rapid transitions r n and n r that coincide with distinct lithological boundaries a fe migration model is presented in which magnetite is formed under different diagenetic conditions during sulphate reduction originally formed primary magnetite is preserved this primary magnetite has recorded the pre transitional normal polarity after burial migration of ferrous iron occurs and subsequent oxidation produces secondary magnetite which records the post transitional reversed polarity and produces the two apparent transitions in addition low temperature lt and high temperature ht components record the reversal in a slightly different way the ht component being acquired with a delay it is probable that both components reside in magnetite but have a different origin and grain size distribution giving different blocking temperature spectra the actual upper cochiti reversal occurs at a level with an estimated astronomically calibrated age of 4 165 ma

provenance discrimination of upper yangtze river basin sediments new insights from heavy mineral signatures and detrital magnetite geochemistry abstract magnetite is typomorphic and its crystal textures and chemical fingerprint form unique signatures that can be used to determine sediment provenance determination of the provenance of sediments in the upper yangtze river is critical for understanding its evolution and the uplift of the tibetan plateau in this study petrographic analysis and electron probe microanalysis epma of 800 detrital magnetite grains were performed to differentiate the provenance of sediments within the mainstream and major tributaries of the upper yangtze river catchment chemical analyses show that the elemental composition of magnetite grains shows pronounced variations among the different sections of the mainstream and tributaries based on the observed chemical fingerprints we infer that the source rocks control the elemental composition of magnetite grains the magnetite contribution is closely related to the tectonics climate and erosion of parent rocks within different drainage basins magnetite from the trunk stream of the jinsha river is found to be a significant contributor to the upper yangtze river magnetite grains of the upper jinsha river are primarily derived from source areas composed of silicic plutonic rocks and ophiolite lithologies that crop out on the se tibetan plateau magnetite grains within the sands of the lower jinshajiang sediments are characterized by high concentrations of ti mg cr al and mn and are derived from the widely distributed emeishan flood basalts and pan xi layered basic ultrabasic igneous rocks this source is also a major contributor of magnetite to the upper yangtze river and the parent rock distributed in this region is of typomorphic significance to the development of the yangtze river the origin of magnetite grains in the tributaries depends on the parent rocks distributed in their catchments in summary the presence of detrital magnetite grains provides valuable information for discriminating the provenance of sediments in the upper yangtze river drainage basins

geochemical and hydrological processes controlling groundwater salinity of a large inland wetland of northwest australia abstract understanding mechanisms of hydrochemical evolution of groundwater under saline and brine wetlands in arid and semiarid regions is necessary to assess how groundwater extraction or injection in large scale basins may affect the natural interface between saline fresh aquifers in those systems we investigated the evolution of groundwater of the fortescue marsh a large inland wetland of northwest australia that is mainly supplied by floodwater from the upper fortescue river catchment the marsh is located in the pilbara region one of the world s major iron ore provinces where mining activities often occur below water tables here we quantified the stable isotope and chemical composition of groundwater surface water and rainfall in and around the marsh to better understand how saline marshes and playa lakes function geochemically hydrologically and ecologically the deep groundwater 50 m depth of the fortescue marsh is highly saline 100 g l 1 whilst shallow groundwater 0 20 m depth and surface water are mainly fresh or brackish currently the marsh is mainly recharged by occasional floodwater consequently salt in the marsh is concentrated by evaporation of rainfall we expected that the hydrochemical composition of surface and groundwater would therefore reflect the chemical composition of rainwater we analysed 206 water samples for stable isotope composition 2 h 18 o and water chemistry including ph dissolved oxygen electrical conductivity ec and total dissolved solids tds as well as na ca mg k si fe hco 3 so 4 cl sr and br we then developed geochemical models and a salt inventory to estimate the geological time of salt accumulation and to decouple geochemical characteristics of salt from modern groundwater we found that groundwater associated with the marsh can be divided into two distinct groups that are characterised by their stable isotope compositions i fresh and brackish groundwater tds 1 18 o 8 0 0 9 and ii saline and brine groundwater tds 10 g l 1 18 o varies from 2 5 to 7 2 fresh groundwater was evaporated by

the groundwater chemistry of the lower mersey basin permo triassic sandstone aquifer system uk 1980 and pre industrialisation urbanisation abstract the lower mersey basin permo triassic sandstone aquifer lies in a heavily urbanised and industrial area of nw england extensive pumping has lowered the piezometric surface considerably causing the sandstone aquifer which is overlain by a variable sequence of glacial deposits to become extensively unconfined the groundwater chemistry of the system appears to be controlled by the geometry of the sandstones faulting the variable distribution and permeability of the quaternary deposits and by the pumping the water in the present day recharge areas is affected by pollution with high no 3 so 4 and cl concentrations it has ph values as low as 4 3 the oldest fresh waters in the area age less than a few thousand years are strongly ion exchanged as a result of the flushing of saline water from the system these waters grade into similar but much less ion exchanged waters with zero no 3 very low so 4 and high hco 3 a fourth group of waters appears to be the result of mixing between the latter waters and pumping induced leakage through the quaternary deposits a final group of waters is characterised by very low alkalinity and is strongly associated with particular geological units poor in carbonates minor ion distributions confirm the patterns suggested by the major ions the distribution of the water chemistry preserves some of the features of the pre pumping system in this low transmissivity high storage system and reconstruction of the pre pumping chemical distributions is attempted to highlight the effects of industrial man on the system

recent fold growth and drainage development the janauri and chandigarh anticlines in the siwalik foothills northwest india the active growth of a fault and thrust belt in frontal zones of himalaya is a prominent topographical feature extending 2500 km from assam to pakistan in this paper kinematical analysis of frontal anticlines and spatial mapping of active faults based on geomorphological features such as drainage pattern development fault scarps and uplifted quaternary alluvial fans are presented we analyse the geomorphic and hydrographic expressions of the chandigarh and the janauri active anticlines in the nw india siwaliks to investigate the morphological scenario during the folding process we used spatial imagery geomorphometric parameters extracted from digital elevation models and fieldwork folding between the beas and sutlej rivers gives clear geomorphological evidence of recent fold growth presumably driven by movements of blind thrust faults structural style within the janauri and chandigarh anticlines is highly variable fault propagation folds pop up structures and transfer faults the approach presented here involves analysis of topography and drainage incision of selected landforms to detect growth of active anticlines and transfer faults landforms that indicate active folding above a southwest dipping frontal thrust and a northeast dipping back thrust are described along strike differences in ridge morphology are measured to describe the interaction of river channel patterns with folds and thrust faults and to define history of anticline growth the evolution of the apparently continuous janauri ridge has occurred by the coalescence of independent segments growing towards each other by contrast systematic drainage basin asymmetry shows that the chandigarh anticline ridge has propagated laterally from nw to se

transverse tectonic structural elements across himalayan mountain front eastern arunachal himalaya india implication of superposed landform development on analysis of neotectonics abstract structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern arunachal sub himalaya mountain front sinuosity smf index values close to one are indicative of the active nature of the mountain front all along the eastern arunachal himalaya which can be directly attributed to the regional uplift along the himalayan frontal thrust hft however the mountain front is significantly sinusoidal around junctions between hft mbt main boundary thrust and active transverse faults the high values of stream length gradient sl and stream steepness ks indices together with field evidence of fault scarps offset of terraces and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults this reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses providing favourable sites for deposition of recent sediments tectonic interactions of these transverse faults with the himalayan longitudinal thrusts mbt hft have segmented the mountain front marked with varying sinuosity the net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements some distinctive examples are in the eastern extremity of ne himalaya across the dibang river valley the nw se trending mountain front is attenuated by the active mishmi thrust that has thrust the mishmi crystalline complex directly over the alluvium of the brahmaputra plains the junction of the folded hft and mishmi thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the dibang river course similarly the transverse faults cut the mountain front along the sesseri siluk siku siang mingo sileng dikari and simen rivers at some such junctions landforms associated with the active right lateral strike slip faults are superposed over the earlier landforms formed by transverse normal faults in addition to linear transverse features we see evidence that the fold thrust belt of the frontal part of the arunachal himalaya has also been affected by the neotectonically active nw se trending major fold known as the siang antiform that again is aligned transverse to the mountain front the folding of the hft and mbt along this antiform has reshaped the landscape developed between its two western and eastern limbs running n s and nw se respectively the transverse faults are parallel to the already reported deep seated transverse seismogenic strike slip fault therefore a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the himalayan region must take into account the role of transverse tectonics

geomorphic response of coastal streams to low intermediate and high rates of uplift medocino triple junction region northern california analysis of three dimensional morphological properties of 24 coastal drainage basins that have evolved in areas of low 3 m 1 000 yr rates of uplift near the mendocino triple junction mtj coastal northern california identified channel gradients as the best indicator of tectonism in the landscape lower order tributaries best reflect tectonically controlled differences the largest streams examined of third order are able to adjust to most base level change and maintain their profile form whereas lower order streams farther upstream tend to accumulate the effects of net base level fall and have steepest profiles in the areas of highest uplift rates variations in steepness of first order channel gradients indicate that 1 high uplift rates in the wake of the mtj have existed for at least 73 000 yr and 2 differential tilt of the region to the north and south of the current locus of highest uplift rate is occurring in association with regional uplift although first order streams are excellent indicators of areas of both high uplift rates and regional differential tilting they are less useful in distinguishing between areas of low and intermediate uplift rate analysis of the longitudinal profile of the main trunk stream of ten of the 24 drainage basins using the stream gradient index was more useful to categorize broadly the uplift rates and to distinguish between streams in low and intermediate uplift rate areas although the hypotheses tested herein do not identify the exact mechanism off uplift in the mtj region they do indicate that the nature of deformation is most likely regional tilt rather than crustal shortening with localized compressional folding and thrust faulting they also indicate that geomorphic responses trail in the wake of the uplift rate response caused by development of a slab window beneath the north american plate 1 maximum uplift rates occur 9 km south of the northern boundary of the slab window 2 maximum mean first order channel gradient occurs 16 km south of the northern edge of the slab window and 3 maximum drainage basin relief occurs 20 km south of the northern edge of the slab window associated lag times between passage of the southern edge of the subducted gorda plate slab and geomorphic responses are 160 000 yr for maximum uplift rates 290 000 yr for maximum channel gradients and 370 000 yr for maximum relief