argon 39 argon 37 and krypton 85 isotopes in stripa groundwaters abstract 39 ar 37 ar and 85 kr activities in groundwater samples from three boreholes in the stripa granite are compared with 222 rn activities and with data from a granitic groundwater in switzerland in situ production rates in bulk granite and in fracture filling minerals are calculated the measured isotopes in groundwater have been produced by nuclear reactions in the rock matrix it was reported earlier that a large fraction of the in situ produced 222 rn can escape to the water phase due to the unusual microscopic distribution of u which seems to be in close contact with the water phase the same conclusion can be drawn for 85 kr with escape factors between 5 and 25 the 39 ar values in stripa groundwaters are the highest measured so far but consistent with the unusually high neutron flux in stripa as compared to granites with lower u and th contents the 37 ar concentrations appear to be quite high but since it is the first time that this isotope has been identified in groundwater the basis for a comparison with different rock formations is still too small it seems possible that calcite fracture fillings in stripa have a major influence on the concentration of 37 ar in groundwater

andean tectonics as a cause for changing drainage patterns in miocene northern south america newdatafromneogenestratainnorthernsouthamericasuggestthatmiocenetectonisminthenortheasternandeswasresponsible for the genesis of the amazon river and changes in the drainage patterns of other major rivers such as the magdalena and the orinoco here we present a new model for the paleogeographic evolution of northern south america during the miocene in the early miocene a large part of the drainage of northwest amazonia was directed northward along the paleo orinoco river system to a deltainlakemaracaibo upliftoftheeasterncordillerainthelate middle miocene caused thefirst development of the amazon river however no connection with the atlantic was established and the amazon fed the paleo orinoco river system which drained toward the caribbean substantial andean uplift in the late miocene resultedinmajorchangesinpaleogeography theorinocochangedits course the amazon established a connection to the atlantic causing the drowning of carbonate platforms and the amazon caribbeanconnectionwasclosed thusthedrainageandpaleogeography ofnorthernsouthamericainthemiocenewerestronglycontrolled by tectonic movements in the northeastern andes

the background concentrations of 13 soil trace elements and their relationships to parent materials and vegetation in xizang tibet china abstract the background concentrations of 13 soil trace elements copper cu lead pb zinc zn cadmium cd nickel ni chromium cr mercury hg arsenic as selenium se cobalt co vanadium v manganese mn and fluorine f from approximately 205 pedons in tibet china are reported here for the first time the 13 trace element concentrations follow an approximately log normal distribution while the mean concentrations of hg and se are lower and as is higher than the average concentration for all of china concentrations of the other trace elements are similar to the national average trace element concentrations are related to vegetation and human activity also played a notable role on the contents of trace elements in tibet the parent material relationship for all 13 soil trace element concentrations follows the pattern shale sandstone igneous rock limestone alluvial sediment glacial deposits lake sediments while for vegetation and human activity the concentration pattern is farmland shrub forests meadow prairie marsh and others the soil trace element concentrations on the tibetan plateau are related primarily to the parent material but were also affected by vegetation and human activity

trace elements of the soil plant systems in subtropical karst and clasolite areas in guilin guangxi china the transfer processes of trace elements within the soil plant system is part of the biochemical cycling of chemical elements representing a flow of elements from nonliving to living compartments in biosphere trace elements distribution in soil plant system is a key issue in assessing their mobility and availability in soils this study was conducted to assess the transfer mechanism of copper cu iron fe manganese mn nickel ni strontium sr and zinc zn in eleven natural plants and associated rhizosphere soils in subtropical karst and clasolite areas southwestern china using inductively coupled plasma atomic emission spectroscopy trace elements except sr are rich in the limestone soil of the karst area whereas they are dispersed in the red soil of the clasolite area moreover their active rates in the limestone soil are greatly reduced compared with the red soil contents of trace elements in plants are both affected by the geochemical and biogeochemical characteristics of trace elements distributions of trace elements are related to plants physiological characteristics trace elements chemical characteristics and geological background as well

trace element contents and correlation in surface soils in china s eastern alluvial plains a study investigating the contents of 13 trace elements and the correlations between these trace elements and soil parameters of the surface soils in the eastern alluvial plains of china is summarized and discussed in this paper the results show that the contents of some elements studied differ from region to region close relations have been noted between all the trace element contents in the soils of the eastern alluvial plains and the relevant surface materials of erosion regions which demonstrate the effects of parent materials while climatic conditions and human interventions are also found to be important factors close relations were found between the transition elements of the quaternary period and the chalcophile elements except cu the chemical and geochemical properties of these elements are identified as beeing important inherent characteristics that affect the relations of these elements in the soils

understanding and modelling dissolved gas transport in the bedrock of three fennoscandian sites summary the origin and transport of dissolved gases in the geosphere is of interest for assessment studies of nuclear waste repositories in this paper we analyse available field measurements of helium methane and hydrogen at three fennoscandian sites forsmark and laxemar in sweden and olkiluoto in finland the field data are interpreted using different analytical models all based on the one dimensional diffusion equation the results of the different models provide estimates about the amount of deep gas flux the in situ production and the groundwater residence time of the considered sites the computed helium fluxes which fall within the lower range of crustal degassing fluxes reported by torgersen 2010 are strictly related with the high tightness of the considered fracture media the very high estimates of groundwater residence time indicate that at the considered depths there are only very few flowing fractures while in the rest of the fractured domain groundwater has been almost motionless during a whole glacial cycle

noble gases in formation fluids from deep sedimentary basins a review abstract atmospheric ne ar kr and xe are observed in fluids occurring in deep basins modifications of their abundance patterns reveal modes of recharge and brine formation phase separations during boiling and association of natural gas with water or oil radiogenic 4 he and 40 ar serve as age indicators of entrapped fluids effective over a significant portion of the geological time scale simultaneous application of 13 c atmospheric noble gases and radiogenic 4 he and 40 ar is recommended to identify a recent bacterial natural gas formation not accompanied by oil and b natural gas formed along with oil in a mature source rock

238u 226ra and 210pb in some vent waters of the galapagos spreading center the concentrations of sup 226 ra sup 238 u and sup 210 pb have been measured in waters from the mussel bed and the rose garden thermal fields at the galapagos spreading center over a temperature range of approx 2 5 16 sup 0 c the sup 226 ra t plots yield slopes of 0 112 and 0 036 dpm kg sup 0 c for the mussel bed and the rose garden respectively yielding a global hydrothermal sup 226 ra flux less than 5 of that required to sustain the oceanic inventory sup 238 u concentration in waters 9 sup 0 c is the same as that in ambient sea water whereas water hotter than approx 9 sup 0 c shows a decreasing trend with temperature to zero sup 238 u at approx 29 sup 0 c sup 210 pb concentration in mussel bed increases with temperature and extrapolated to approx 350 sup 0 c yields a sup 210 pb concentration considerably less than that expected from sup 222 rn decay and basalt alteration

uranium isotopes and 226ra content in the deep groundwaters of the tri state region u s a abstract uranium isotopes have been analyzed in a number of water samples from the groundwater flow system of the cambro ordovician aquifers in the tri state region of missouri kansas and oklahoma u s a the system consists of sodium chloride water having low uranium content 0 04 g l which meets westward flowing calcium bicarbonate water having uranium content about an order of magnitude greater in a transitional zone located just to the west of the missouri kansas border in the area where the waters mix and then flow south westward h2s is commonly found in the water 226ra is relatively high and uranium concentration is lower than to the east it appears that at least part of the dissolved uranium in the westward flowing water is precipitated in the zone of mixing because the dissolved uranium has 234 u 238 u activity ratio of 7 10 any precipitated uranium would have an enhanced capability of generating the daughter 226ra however the distribution of uranium isotopes within the system suggests that the source of radium in the water of the transitional zone is not the inferred present day zone of uranium accumulation but rather the brines themselves

uranium geochemistry in geopressured geothermal aquifers of the u s gulf coast formation water from u s gulf coast geopressured geothermal sandstone aquifers has been analyzed to determine the geochemistry of uranium in these systems results of chemical analyses and chemical equilibrium modeling indicate the formation waters are in equilibrium with uraninite uo2 and coffinite usio4 the 234u238u activity ratios in the formation waters range from 1 06 to 1 69 these isotopic data suggest that at formation temperatures uranium is continually reequilibrating chemically and isotopically between water a solid phase of either uo2 or usio4 and a component of 234u supplied to solution from the aquifer matrix material by alpha recoil processes

stream capture as driver of transient landscape evolution in a tectonically quiescent setting we use unique fluvial gravel deposits preserved atop a regional drainage divide to confirm the role of stream capture in driving 250 m of incision in the transient roanoke river basin of the appalachian mountains united states gravel provenance constrains the pre capture position of the divide indicating that 225 km 2 of basin area were abruptly connected to the base level of the capturing stream the resulting wave of incision is currently manifest as major knickzones separating adjusting reaches from relict headwaters resembling streams of the new river basin from which the roanoke river was captured the unusual preservation of the unconsolidated gravels on small relict surfaces adjacent to bedrock gorges indicates extreme spatial variability in erosion rates within the roanoke basin which is the first documented example of a transient passive margin basin connected to a capture event by stranded fluvial debris our results show the potential for stream capture across an asymmetric drainage divide to drive major transient incision independent of external forcings such as climate change or tectonic uplift a continuation of this process will lead to eventual capture of 7000 km 2 of the new river basin in the relatively near geologic future

fracturing induced release of radiogenic 4he and 234u into groundwater during the last deglaciation an alternative source to crustal helium fluxes in periglacial aquifers external 4he sources have been invoked to explain 4he concentrations in groundwater greater than those expected from in situ u and th production in a fractured aquifer of ordovician age located in the st lawrence lowlands quebec canada 4he concentrations of up to 4 48 x 10 5 cm3 stp gh20 1 were measured such concentrations are ca 1000 times higher than would be expected from in situ production a concomitant increase in 4he concentration and 234u 238u activity ratio is shown suggesting a common release process in groundwater for 234u and 4he this process has tentatively been identified as glaciation induced rock fracturing following the laurentide ice sheet retreat the resulting increase in exposed grain surface facilitates 234u release by recoil and that of radiogenic 4he by diffusion using a model of helium diffusion from a spherical grain it is shown that rock fracturing facilitated the release of accumulated 4he at rates ranging from 4 2 x 10 10 cm3stp gh20 1 yr 1 to 1 06 x 10 8 cm3stp gh20 1 yr 1 these release rates are between 1 000 and 30 000 times higher than the local u and th steady state production rate of 3 5 1 4 x 10 13 cm3stp grock 1 yr 1 integration of 4he release rates over time yields a radiogenic 4he concentration of between 3 85 x 10 6 cm3stp gh20 1 and 7 12x 10 5 cm3stp gh20 1 in the range of concentrations measured in the st lawrence lowlands fractured aquifers results support the occurrence of a local radiogenic helium source to explain the excesses measured in groundwater without requiring a significant external he crustal flux

the southern limit of cordilleran ice in the colville and pend oreille valleys of northeastern washington during the late wisconsin glaciation the southern limit of the lobes of the cordilleran ice sheet in the colville and pend oreille valleys of northeastern washington during the late wisconsin fraser glaciation has been placed at widely different positions by various investigators the confusion that resulted in these different positions is due to the fact that both lobes at times terminated in glacial lakes and much of the terminal area of the pend oreille river lobe was swept by floods from glacial lake missoula evidence presented in this paper of the southern limit of these two lobes during the late wisconsin glaciation consists of i the southern limit of late wisconsinan till ii the southern limit of lateral meltwater channels iii meltwater channels whose headward areas coincide with the southern limit of late wisconsinan till and iv reconstructed ice surface profiles this evidence suggests that the southern limit of the colville lobe is represented by a moraine near the town of springdale whereas that of the pend oreille river lobe is near the town of newport the timing and extent of late wisconsinan deglaciation in the colville valley are provided by radiocarbon ages and late pleistocene tephras at sites upglacier from the terminal position these data demonstrate that the colville lobe had retreated at least 50 km by about 12450 bp in the pend oreille valley the presence of a glacier peak tephra layer near the town of ione indicates that the pend oreille river lobe had retreated at least 70 km prior to deposition of the tephra

the implications of laboratory222rn flux measurements to the radioactivity in groundwaters the case of a karstic limestone aquifer laboratory time scale experiments were conducted on carboniferous limestone gravels from the mendip hills area england with the purpose of evaluating the release of 222 rn to the water phase the specific surface areas of the samples were 4 14 and 1 69 cm 2 g 1 which provided respectively values of 50 6 and 12 7 pci for the released rn these results allowed the calculation of the emanation coefficient of this rock matrix with respect to the release of rn where completely different values corresponding to 23 and 6 were found suggesting that the extent to which grain boundaries or imperfections in aggregates of micro crystals of calcite intersect the particle surface certainly affects the rn release they also permitted the evaluation of models for the generation of rn in rocks and transfer to water in order to interpret the radioactivity due to this gas in groundwaters from the karstic aquifer of the mendip hills area where the calculated activities in groundwater based on the values of 23 and 6 for the emanation coefficient were about 51 and 15 times higher than actually measured in groundwater therefore the emanation coefficient in nature is considerably smaller than in the lab experiment and another factor k 0 k 1 may be introduced into the equations related to the modelling with the aim of adjusting the theoretical practical results

late quaternary river drainage and fish evolution southland new zealand late quaternary to holocene landscape evolution in southern new zealand was dominated by glacial outwash processes evolution of the drainage network on a regional scale was punctuated by numerous river capture events associated with outwash transport and deposition river capture events can be inferred from geological and topographic observations throughout the region independent evidence for river capture and drainage reorientation can be obtained from genetic studies of a freshwater limited fish galaxias southern informal name regionally extensive interlinking of principal rivers mataura oreti aparima via coalescence of alluvial plains onshore and offshore at sea level lowstands has resulted in a widespread genetic homogenisation of fish populations b 0 9 mtdna divergence genetically similar populations of g southern are present in an adjacent catchment von that was captured episodically by the neighbouring major river system clutha the low degree of genetic divergence between oreti and von catchments b 0 15 mtdna divergence demonstrates that genetic interaction between fish populations was severed recently probably during the early holocene this is in accord with radiocarbon dating 11 13 ka of the youngest gravel level within the intervening divide in contrast morphologically similar fish in another adjacent major river waiau have a minimum mtdna divergence of 2 4 from the fish in the mataura oreti and aparima rivers this genetic separation occurred at ca 145 240 ka based on the late quaternary outwash terrace dating in agreement with molecular clock estimates geological and genetic data in combination provide powerful tools for the elucidation of local and regional geomorphic evolution where river capture is an important process the potential is strong for genetic data alone to provide information on the relative and absolute timing of river capture events but must be interpreted in the context of severance of water connections between catchments and subsequent isolation of freshwater limited populations 2006 elsevier b v all rights reserved

radium precipitation and extreme 238u series disequilibrium along the dead sea coast israel abstract very intense gamma ray emissions produced by nuclides in the 238 u decay series were measured in active and relict spring deposits along the dead sea coast precipitates of ra near sites of modern springs provide a local source of rn to coexisting waters relict spring deposits representing prior dead sea levels contain high concentrations of ra the ra in both cases has been derived from the dead sea waters or from the dead sea in combination with a ra component from the primary spring water and coprecipitated with hydrous oxides of mn and fe the metal oxides precipitated in response to the mixing of the fresher spring waters with the dead sea brine

uranium series disequilibrium in a young surficial uranium deposit northeastern washington u s a a recently discovered ore grade accumulation of u in organic rich sediments of late quaternary age provides an opportunity for studying the early association of u u daughters and organic matter in a natural setting the u occurs in valley fill sediments of peat peaty clay silt and sand along the north fork of flodelle creek stevens county washington radiometric techniques delayed neutron high resolution gamma ray spectrometry thin source alpha spectrometry were employed to determine the abundance and distribution of u series nuclides the extent of secular equilibrium within the u decay series and the apparent u series ages of u incorporation sixteen lithologically distinct intervals were sampled from a 292 cm core uranium contents range from 140 to 2790 ppm and are positively correlated with organic contents measured alpha activity ratios of 234u 238u 1 31 1 38 are very similar to those reported in coexisting waters suggesting a rather constant isotopic composition of introduced u much lower th contents of 10 40 ppm are controlled by the type and abundance of silicate detritus the youth of the host sediments 15 000 a and the paucity of associated radioactivity suggested large excesses of u relative to radioactive daughters and such excesses were observed particularly in the shallowest intervals apparent ages of u emplacement determined by the alpha activity ratio of 230th daughter to 234u parent show a general increase with depth and fair agreement with estimated depositional ages this observation suggests dominantly syndepositional or early post depositional emplacement of u followed by decay generated buildup of 230th daughter with time however interval by interval comparisons of the relative abundances of other daughters particularly 226ra and 210pb indicate variability caused by processes other than closed system growth and decay probably because chemically diverse daughters that are decay generated in situ have differing mobilities and because upwelling ground water continuously adds more u and minor amounts of daughters if 230th is considered the least susceptible to these modifications the data suggest some addition of 234u in the deepest intervals and some loss of 226ra and or gain of 222rn throughout the studied core

divide migration in response to asymmetric uplift insights from the wula shan horst north china abstract drainage divides play significant roles in shaping landscapes nevertheless they are not static through space and time previous numerical models have demonstrated divide motions in response to asymmetric tectonic uplift however natural examples that have nicely recorded these processes and hence could verify the results of numerical simulations are still lacking in this contribution we integrate the results of digital elevation models dems based morphotectonic analysis with the tectonic landforms observed during field surveys to investigate the status of topography and probable drainage evolution history of the wula shan shan means mountain s in chinese a roughly west east trending horst block bounded by normal faults in the hetao graben north china the results demonstrate that the differences of obtained geomorphic indices are significant between the southern and northern drainage basins higher hypsometric integral hi and normalized channel steepness ksn values and lower ratios of valley floor width to valley height vf indicate higher tectonic uplift rate at the southern flank the main divide of the wula shan had migrated northward which was probably caused by the decrease of asymmetry in vertical uplift associated with the margin faults we suggest the results of this study may shed new light on divide mobility as well as landscape evolution in actively extending regions

scanning and transmission analytical electron microscopy stem edx can identify structural forms of lead by mapping of clay crystals abstract to increase the analytical precision in identifying structural forms of heavy metals it is necessary to refine the methodology for analysis of mineral crystals the aim of this study was to characterize clay crystals in soils and relate their mineralogy to the structural occurrence of pb using scanning transmission electron microscopy stem together with energy dispersive x ray edx spectrometry we sampled soils from two areas naturally rich in heavy metals with known occurrences of mineral deposits pbs in carbonate and phyllite mica schist rocks there was an association of p with pb and the main mineral phase containing pb in the soil clay fractions was plumbogummite no associations between pb and fe oxides were observed secondary phyllosilicate minerals such as kaolinite and smectite did not contain structural pb there was isomorphous substitution of ti by pb in an anatase crystal despite the differences in ionic radii the chemical analysis of individual crystals by stem edx was hampered by the high occurrence of microaggregates of clay minerals

radiogenic helium in shallow groundwater within a clay till southwestern ontario 1 profiles of 4he in pore water were measured in clay aquitards in sw ontario the 4he distributions are consistent with groundwater velocities that are 70 of initial 4he for 50 to 60 ka prior to incorporation into the till

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

high magnitude and rapid incision from river capture rhine river switzerland 1 landscape evolution is controlled by the development and organization of drainage basins as a landscape evolves drainage reorganization events can occur via river capture or piracy whereby one river basin grows at the expense of another the river downstream of a capture location will generate a transient topographic response as the added water discharge increases sediment transport and erosion efficiency this erosional response will propagate upstream through both the captured and original river basins here we focus on quantifying the impact of drainage reorganization along the rhine aare river system 45 000 km2 during the late pliocene early pleistocene where gravel remnants indicate total incision of 650 m during the last 4 2 myr in the region of the recent aare rhine confluence we develop a numerical model of drainage capture to quantify the range of possible magnitudes of erosion and the transient river response resulting from the reorganization of the rhine river the model accounts for both fluvial incision and sediment transport our model estimates 400 800 m of river elevation change lowering profiles during the last 4 myr due to river capture events providing an important component to the recent exhumation budget of the swiss alpine foreland the model indicates a rapid response to capture events re equilibration timescale of 1 myr the predicted incision magnitudes are consistent with incision measured from the elevation of pliocene and early pleistocene river gravels suggesting that across northern switzerland a significant amount of incision can be explained by drainage reorganization

the geochemistry of water near a surficial organic rich uranium deposit northeastern washington state u s a abstract the chemistry of three stream three spring and six near surface waters in the vicinity of a holocene organic rich uranium deposit is described with particular emphasis on the chemistry of u results characterize the solution behavior of uranium as u bearing water interacts with relatively undecomposed surficial organic matter of the measured major and trace chemical species only u is consistently highly enriched 17 318 ppb relative to reported values for regional waters or to literature values for waters in largely granitic terrains r mode factor analysis of the chemical data suggests that most u is present in a soluble form but that some u is also associated with fine suspended particulates of clay organic matter or hydrous oxides calculations that apply thermodynamic data to predict u speciation in solution indicate the relative importance of uranyl carbonate and uranyl phosphate complexes analysis of more finely filtered samples 0 05 m vs 0 45 m and direct radiographic observations using fission track detectors suspended in the waters indicate the presence of some uraniferous particulate matter application of existing thermodynamic data for uranous and uranyl bearing minerals indicates that all waters are undersaturated with u minerals as long as ambient eh 0 1 v if coexisting surface and near surface waters are sufficiently oxidizing initial fixation of u in the deposit should be by a mechanism of adsorption alternatively more reducing conditions may prevail in deeper pore waters of the organic rich host sediments perhaps leading to direct precipitation or diagenetic formation of u4 minerals a 234 u 238 u alpha activity ratio of 1 08 0 02 in a spring issuing from a hillslope above the deposit suggests a relatively soluble source of u in contrast higher activity ratios of 234 u 238 u 1 3 in waters in contact with the uraniferous valley fill sediments suggest differences in the nature of interaction between groundwater and the local u rich source rocks

accumulations of major and trace elements in particle size fractions of soils on eight different parent materials abstract the major me and trace element te contents of virgin soils are very important in areas with chances to be contaminated from anthropogenic activities we determined the me and te composition of 21 soils developed on dacite lamproite andesite basalt diabase mica schist quartzite and colluvial deposits to elucidate elemental transfer from pgm to soils we also studied the enrichment of me and te in various particle size fractions in general the highest content of si was observed in sand fraction regardless of pgm and is attributed to the dominance of quartz sio 2 in this size fraction results showed that pb cd cu and zn are associated with al and or fe containing minerals such as micas pyroxenes and amphiboles and exhibit preferential partitioning into fine particle size fractions in the soils studied cobalt ni and cr are associated with mg bearing minerals such as smectites and ti is related to na bearing mineral such as plagioclases e g albite and andesine significant correlations between elemental contents in soils and pgm confirm that rock types significantly control me and te contents in soils although some variations are expected due to factors such as resistance of rock to weathering formation of secondary fe oxides elemental fixation and other pedogenic processes our data can be used to as benchmark or background information for me and te contents to assess any elemental enrichment from anthropogenic activities

natural radioelement solution by circulating groundwaters in the stripa granite natural radioelement concentrations in groundwaters from the fracture flow regime in the stripa granite were monitored during the period 1977 1986 uranium concentrations from depths of 80 m or less and in minewaters from above the hydraulic sink produced by the deepest mining level 410 m range from 10 to 90 ppb 234u238u activity ratios are characteristic of chemical leaching processes at the shallower depths whilst at about 350 m groundwaters occur which have an additional component of 234u by alpha recoil processes at greater depths u concentrations are indicative of the changed redox conditions and are subject to activity ratio enhancement by the alpha recoil process groundwater residence times may be estimated from the rate of such recoil solution of 234u in zones where chemical leaching of u is not active the 222rn contents of the minewaters are extremely high and can be related to the 222rn flux from fracture surfaces and the fracture width the fracture apertures range from 10 mm for the shallow groundwater zone 222rn contents m for water from the deepest borehole section 222rn content 100 kbq kg 1 the activity ratios 234th238u 210pb222rn and 210po222rn have been used to estimate residence times for th pb and po isotopes solution of ra is controlled by chemical rather than alpha recoil processes the 226ra content of the groundwater increases with salinity and is well correlated with groundwater ca content the 228ra226ra activity ratios in the groundwaters suggest that water rock interaction occurs predominantly with the average granitic matrix rather than with highly uraniferous fracture mineralisation the behaviour of ra th and po isotopes may be used to assess that of homologous fission product and actinide constituents of nuclear wastes in groundwaters

evaluation of pleistocene groundwater flow through fractured tuffs using a u series disequilibrium approach pahute mesa nevada usa abstract groundwater flow through fractured felsic tuffs and lavas at the nevada national security site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at pahute mesa to help evaluate fracture flow and matrix water exchange we have determined u series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces breccia zones and interiors of unfractured core the u series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium series decay chain due to preferential mobilization of 234 u relative to 238 u and u relative to th samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays silica fe mn oxyhydroxides and zeolite intact core interiors and breccia fragments were sampled in bulk in addition profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture matrix water exchange samples of rock matrix have 234 u 238 u and 230 th 238 u activity ratios ar closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix greater u mobility was observed in welded tuff matrix with elevated porosity and in zeolitized bedded tuff samples of brecciated core were also in secular equilibrium implying a lack of long range hydraulic connectivity in these cases samples of discrete fracture surfaces typically but not always were in radioactive disequilibrium many fractures had isotopic compositions plotting near the 230 th 234 u 1 1 line indicating a steady state balance between u input and removal along with radioactive decay numerical simulations of u series isotope evolution indicate that 0 5 to 1 million years are required to reach steady state compositions once attained disequilibrium 234 u 238 u and 230 th 238 u ar values can be maintained indefinitely as long as hydrological and geochemical processes remain stable therefore many pahute mesa fractures represent stable hydrologic pathways over million year timescales a smaller number of samples have non steady state compositions indicating transient conditions in the last several hundred thousand years in these cases u mobility is dominated by overall gains rather than losses of u

evaluation of arsenic sorption and mobility in stream sediment and hot spring deposit in three drainages of the tibetan plateau abstract enrichment of arsenic as in sediment 12 227 mg kg in the upstream tributaries of the indus and brahmaputra rivers originating from the tibetan plateau where hot springs were abundant has been found sandy sediment samples from the nu salween river lantsang mekong river and jinsha yangtze river also originating from the tibetan plateau were collected in july 2012 and were found to contain 6 8 mg kg to 30 5 mg kg as average17 3 6 5 mg kg n 12 deposits collected within 1 m of two hot springs in changdu tibet displayed significantly higher as levels 263 7 mg kg in ld 2 with 65 quartz and 101 8 mg kg in nud 1 with 82 calcite to evaluate the valence states of as and also the phases responsible for sorption x ray absorption spectroscopy xas was employed to analyze the two hot spring deposits and three river sediment samples coarse sand nud 6 as 14 6 mg kg fine sand nud 4 as 17 8 mg kg and silty sand ld 1 as 30 5 mg kg the x ray absorption near edge spectrum xanes data indicate that 70 of as from 3 samples in the nu salween river drainage nud 1 nud 4 and nud 6 is as v or arsenate with the rest being as 0 or as fe sulfides the proportion of as v is 90 for 2 samples in the lantsang mekong river drainage ld 1 and ld 2 linear combination fit of the iron extended x ray fine structure spectrum exafs show that 3 samples from the nu salween river contain 20 ferrihydrite and 10 goethite without any hematite being detected but 2 samples from the lantsang mekong river contain

a borehole methodology for hydrogeochemical investigations in fractured rock research into the development of borehole techniques for hydrogeochemical investigations in fractured rock has resulted in the construction of a geochemical probe controlled and operated with an umbilical cable system this probe has been field tested to a depth of 600 m in a multilevel ported casing at the chalk river nuclear laboratories crnl the probe provides in situ measurements of ph redox potential dissolved oxygen temperature conductivity and pressure while allowing groundwater sample collection both at surface and downhole the multilevel ported casing preserves the subsurface hydrogeochemical zonation and facilitates sampling at various depths in the crnl borehole dilute na hco3 and na cl waters ranging in age from 500 to 12 000 years have been observed in gneissic rock at depths of 85 to 350 m however accurate hydrogeochemical characterization of the low permeability metagabbro present from 400 to 600 m has been frustrated by contamination from casing installation water

splitting rivers at their seams bifurcations and avulsion river bifurcations are critical but poorly understood elements of many geomorphological systems they are integralelements of alluvial fans braided rivers fluvial lowland plains and deltas and control the partitioning of water and sediment throughthese systems bifurcations are commonly unstable but their lifespan varies greatly in braided rivers bars and channels migrate splitand merge at annual or shorter timescales thereby creating and abandoning bifurcations this behaviour has been studied mainly bygeomorphologists and fluid dynamicists bifurcations also exist during avulsion the process of a river changing course on afloodplain or in a delta which may take 102 103years and has been studied mainly by sedimentologists this review synthesizesour current understanding of bifurcations and brings together insights from different research communities and different environmen tal settings we consider the causes and initiation of bifurcations and avulsion the physical mechanisms controlling bifurcation andavulsion evolution mathematical and numerical modelling of these processes and the possibility of stable bifurcations we end thereview with some open questions copyright 2012 john wiley sons ltd

morphodynamic assessment of side channel systems using a simple one dimensional bifurcation model and a comparison with aerial images side channel construction is a common intervention applied to increase a river s conveyance capacity and to increase its ecological value past modelling efforts suggest two mechanisms affecting the morphodynamic change of a side channel 1 a difference in channel slope between the side channel and the main channel and 2 bend flow just upstream of the bifurcation the objective of this paper was to assess the conditions under which side channels generally aggrade or degrade and to assess the characteristic timescales of the associated morphological change we use a one dimensional bifurcation model to predict the development of side channel systems and the characteristic timescale for a wide range of conditions we then compare these results to multitemporal aerial images of four side channel systems we consider the following mechanisms at the bifurcation to be important for side channel development sediment diversion due to the bifurcation angle sediment diversion due to the transverse bed slope partitioning of suspended load mixed sediment processes such as sorting at the bifurcation bank erosion deposition due to vegetation and floodplain sedimentation there are limitations to using a one dimensional numerical model as it can only account for these mechanisms in a parametrized manner but the model reproduces general behaviour of the natural side channels until floodplain forming processes become important the main result is a set of stability diagrams with key model parameters that can be used to assess the development of a side channel system and the associated timescale which will aid in the future design and maintenance of side channel systems

uranium series disequilibrium in young surficial uranium deposits in southern british columbia disequilibrium studies involving the determination of total u and the activity ratios of 234u 238u and 234u 230th or activities of 230th 226ra and 210pb were carried out on samples from three surficial generally within 5 m of the surface uranium deposits in south central british columbia that give apparent 234u 230th ages of 1000 20 000 years as a result of the young ages the deposits have not yet reached radioactive secular equilibrium and therefore yield very little gamma activity the deposits formed from groundwaters that leached labile uranium from intermediate to felsic igneous rocks two accumulation mechanisms concentrate the uranium evaporation and adsorption onto organic matter the uranium content and the activities of the various daughter nuclides are highly variable within and between the various deposits studied some of the variations can be explained in terms of the accumulation processes in the evaporative process the highest value of uranium and daughter nuclides will be found a

the occurrence and behavior of radium in saline formation water of the u s gulf coast region abstract radium has been measured in deep saline formation waters produced from a variety of u s gulf coast subsurface environments including oil reservoirs gas reservoirs and water producing geopressured aquifers a strong positive correlation has been found between formation water salinity and ra activity resulting from the interaction of formation water with aquifer matrix ra isotopes enter the fluid phase after being produced by the decay of parent elements u and th which are located at sites on and within the solid matrix processes that are belived to be primarily responsible for transferring ra from matrix to formation water are chemical leaching and alpha particle recoil factors controlling the observed salinity ra relationship may be one or a combination of the following factors a ion exchange b increased solubility of matrix silica surrounding ra atoms coupled with a salinity controlled rate of reequilibration of silica between solution and quartz grains and c the equilibration of ra in solution with detrial barite within the aquifer no difference was found in the brine ra relation in water produced from oil or gas wells and water produced from wells penetrating only water bearing aquifers although the relation was more highly correlated for water bearing aquifers than hydrocarbon containing reservoirs

234u238u and 230th234u activity ratios in mineral phases of a lateritic weathered zone abstract a selective phase extraction procedure was developed for the identification of the significant phases of a typical deep soil profile sampled in the vicinity of the ranger no 1 uranium ore body alligator rivers region n t australia the significant phases were identified as amorphous iron oxide crystalline iron oxide and a clay quartz resistate the distribution of 238 u 234 u 230 th and 226 ra between the phases was measured the results indicated that the amorphous iron oxide phase is in adsorption desorption equilibrium with the ground water the crystalline iron oxide phase contains a chemical control the kinetics of which are commensurate with or less than the half life of 230 th 7 52 10 4 y the clay quartz resistate is enriched in 238 u descendants in such a way that they are not readily accessible to the ground water

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

river piracy and drainage basin reorganization led by climate driven glacier retreat river piracy the diversion of the headwaters of one stream into another one can dramatically change the routing of water and sediment with a profound effect on landscape evolution stream piracy has been investigated in glacial environments but so far it has mainly been studied over quaternary or longer timescales here we document how retreat of kaskawulsh glacier one of canada s largest glaciers abruptly and radically altered the regional drainage pattern in spring 2016 we use a combination of hydrological measurements and drone generated digital elevation models to show that in late may 2016 meltwater from the glacier was re routed from discharge in a northward direction into the bering sea to southward into the pacific ocean based on satellite image analysis and a signal to noise ratio as a metric of glacier retreat we conclude that this instance of river piracy was due to post industrial climate change rapid regional drainage reorganizations of this type can have profound downstream impacts on ecosystems sediment and carbon budgets and downstream communities that rely on a stable and sustained discharge we suggest that the planforms of slims and kaskawulsh rivers will adjust in response to altered flows and the future kaskawulsh watershed will extend into the now abandoned headwaters of slims river and eventually capture the kluane lake drainage river piracy the diversion of one stream s headwaters into another has occurred on long timescales an analysis of streamflow and digital elevation models documents river re routing in response to glacier retreat in yukon canada in may 2016

seafloor fluid seeps on kimki ridge offshore southern california links to active strike slip faulting abstract the kimki ridge fluid seeps are located in western catalina basin about 60 km southwest of the southern california mainland and at a water depth of approximately 1100 m multichannel seismic reflection profiles collected by the u s geological survey usgs in 2014 show acoustic transparency within the kimki ridge suggesting the possibility of fluid seeps and possible sub seafloor fluid pathways subsequent multibeam bathymetric and backscatter intensity data collected during a cooperative university of washington usgs cruise in early 2016 show subtle seafloor buildups with high acoustic backscatter reflectivity in three places along kimki ridge supporting the existence of fluid seepage a remotely operated vehicle rov dive conducted as part of the nautilus exploration program took place in august 2016 to confirm the presence of these previously unknown seeps and document their characteristics as well as those of any associated biological communities two of the three seeps were explored by rov and showed abundant evidence of fluid seepage including characteristic algal mats chemosynthetic clams and authigenic carbonate formation the seeps are comprised of carbonate buildups 1 3 m thick and 300 500 m across within these areas we interpret broad crater like depressions 30 50 m across and 1 2 m deep to be individual seep vents the seep areas appear to be broad zones of diffuse seepage that support chemosynthetic biologic communities however active venting was not observed geochemical analyses of rock samples collected from the seeps indicate microbially driven anaerobic oxidation of methane at or near the sediment water interface seismic reflection profiles show chimney like fluid pathways along the limbs and in the axis of the fold forming kimki ridge and evidence of methane in shallow sediments can be traced into the adjacent catalina basin a system of closely spaced faults located at the axis of the kimki ridge anticline may serve as pathways to allow fluid flow to the seafloor our data are consistent with other studies that suggest that transpression is an important component in the formation and localization of fluid seeps in a strike slip setting implying that seep formation may be a common occurrence at fault stepovers or transpressional bends in strike slip systems

radioisotope dynamics the origin and fate of nuclides in groundwater the use of radionuclides as clocks for groundwater dating and as probes to investigate the geometry and spatial extent of the contact area between rocks and water is reviewed subsurface production rates for 222 rn 37 ar 55 kr 39 ar 36 cl 3 he 4 he and 40 ar in various rock types are listed measured rn fluxes from the surface of sandstone grains and from pieces of granite point to scale dependent diffusion coefficients the temporal evolution of subsurface produced 222 rn 37 ar 85 kr and 39 ar activities in groundwaters yields radionuclide escape factors between 0 1 and 9 for the stripa granite sweden and between 1 and 4 for the milk river sandstone canada the combination of 3 h 85 kr 39 ar 14 c 36 cl 4 he in the uk triassic sandstone aquifer allows groundwater dating up to 40 000 a very old groundwaters can be studied using cl 36 cl and 4 he evolution as demonstrated in the milk river aquifer in canada

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

radioelements radiogenic helium and age relationships for groundwaters from the granites at stripa sweden abstract the solution of radioelements and radiogenic 4he by groundwaters in fractured rocks is dependent upon the radioelement distribution in the rock matrix and the extent of the rock water interface the 234 u 238 u activity ratio and the dissolved u rn and he contents of such groundwaters respond to changes in the flow regime with time although 234 u 238 u activity ratios change with groundwater residence time as a consequence of 234th recoil induced solution of 234u the activity ratio is strongly influenced by the u distribution within fractures by the extent of the rock water interface and by the amount of 238u in solution a model for the quantitative evaluation of these effects is presented groundwaters from depths up to 880 m in the stripa granite have variable dissolved uranium contents and 234 u 238 u activity ratios the uranium geochemistry is primarily determined by variations in flow path rather than by groundwater age dissolved radiogenic 4he in the groundwaters increases with their depth of origin and is dependent upon the u content of the granite and upon its fracture porosity it increases with groundwater residence time but movement of 4he by diffusion and transport processes make the actual groundwater age indeterminate

distinguishing seawater from geologic brine in saline coastal groundwater using radium 226 an example from the sabkha of the uae article sabkhat salt flats are common geographic featuresof low lyingmarinecoastalareas thatdevelopunder hyper aridclimaticconditions theyare characterizedby thepresenceof highlyconcentratedsalinesolutions and evap oritic minerals and have been cited in the geologic literature as present day representations of hyper arid regional paleohydrogeology paleoclimatology coastal processes and sedimentation in the geologic record it is therefore important that a correct understanding of the origin and development of these features be achieved knowledge of the source of solutes is an important first step in understanding these features historically two theories have been advanced as to the main source of solutes in sabkha brines an early concept entailing seawa ter as the obvious source and a more recent and dynamic theory involving ascending geologic brine forced upward into the base of the sabkha by a regional hydraulic gradient in the underlying formations ra 226 coulduniquely distinguish betweenthese sourcesunder certain circumstances asitistypically present atelevat ed activity of hundreds to thousands of bq m 3 becquerels per cubic meter in subsurface formation brines at exceedingly low activities in open ocean and coastal water and not significantly supplied to water from recently formed marine sedimentary framework material the coastal marine sabkha of the emirate of abu dhabi was used to test this hypothesis the distribution of ra 226 in 70 samples of sabkha brine mean 700 bq m 3 7 sam ples of underlying deeper formation brine mean 3416 bq m 3

relevance of a lithogeochemical database to epidemiological studies in central saskatchewan canada abstract archived drill cuttings of cretaceous sedimentary rocks from 96 wells were analyzed to provide a geochemical database and maps of a 100 000 km 2 area of bedrock in central saskatchewan a dark shale the white speckled shale is enriched in ca cd mo se u and v and to a lesser degree in as cu ni sb sr and zn when compared to other geological strata in the district this shale subcrops beneath glacial drift near henribourg where there is a coincidence of structural weakness and formation water discharge because groundwater chemistry is controlled mostly by rock and sediment chemistry the possibility was examined that the enrichment of some elements in the white speckled shale may have a bearing on the high incidence of childhood homes of multiple sclerosis patients at henribourg the lithogeochemical study provides basic data that may be of use in epidemiological studies

effect of geo pedological conditions on the distribution and chemical speciation of selected trace elements in forest soils of western alborz iran abstract geologic and pedologic controls have an important influence on the abundance distribution and behavior of elements in natural soil environments in order to assess the role of these factors on distribution and chemical speciation of selected trace elements in soil soils on six parent materials including phyllite tonalite peridotite dolerite shale and limestone were sampled in western alborz in iran soil genesis and development of representative residual pedons were studied for each parent material and the total content of si al fe ca mg co cr cu mn ni pb v and zn were compared enrichment depletion patterns of trace elements were assessed using ti as the reference element and lowest horizon as the reference layer a modified bcr european community bureau of reference sequential extraction procedure was used to fractionate the elements into four operationally defined species the total contents of co cr ni and v are highest in soils derived from peridotite 53 984 285 and 204 mg kg 1 respectively and dolerite 39 1023 176 and 185 mg kg 1 respectively lead and zn contents are highest in soils derived from shale 27 and 106 mg kg 1 respectively which is probably due to the high sorption capacity of clay different elements exhibited very different enrichment depletion patterns in a given pedon moreover depth distribution patterns differed also for a given element among soils with different parent material and even showed considerable variation among soils with similar lithology lead zn cu and mn have been generally enriched in most pedons except in some acidic and strongly leached soils whereas co cr fe ni and v have been leached especially from dystrudepts and eutrudepts the latter elements however showed enrichment trend in hapludalfs and argiudolls parallel to the development of illuvial b horizons iron cr cu ni v and zn are present primarily in the residual fraction independent of soil and parent material type whereas mn pb and co were mainly present in the non residual fractions of most pedons trace element concentrations in the soils of the study area are related primarily to the parent material type while pedogenic processes appear to have played a minor role

uranium isotopes as tracers of groundwater evolution in the complexe terminal aquifer of southern tunisia abstract the complexe terminal ct multi layer aquifer is formed by neogene paleogene sand deposits upper senonian campanian maastrichtian limestones and turonian carbonates the chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the ct aquifer in southern tunisia we paid special attention to the variability of uranium contents and isotopes ratio 234u 238u to provide a better understanding of the evolution of the groundwater system uranium concentrations range from 1 5 to 19 5 ppb typical of oxic or mildly reducing conditions in groundwaters the lowest concentrations are found southeast of the study area where active recharge is supposed to take place when looking at the isotope composition it appears that all the samples including those from carbonate levels are in radioactive disequilibrium with significant 234u excess a clear cut distinction is observed between turonian and senonian carbonate aquifers on the one hand with 234u 238u activity ratios between 1 1 and 1 8 and the sandy aquifer on the other hand showing higher ratios from 1 8 to 3 2 the distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation water rock interaction and mixing between waters having different isotopic signatures significant relationships also appear when comparing the uranium distribution with the major ions composition it is noticeable that uranium is better correlated with sulfate calcium and magnesium than with other major ions as chloride or bicarbonate the 14c activities and 13c values of dic cover a wide range of values from 1 1 pmc to 30 2 pmc and from 3 6 to 10 7 respectively 14c model ages estimated by the fontes and garnier model are all younger than 22 ka and indicate that the recharge of ct groundwater occurred mainly during the end of the last glacial and throughout the holocene

234u and238u concentration in brine from geopressured aquifers of the northern gulf of mexico basin abstract the 234 u and 238 u concentration in brine from six gulf coast geopressured aquifers has been determined the results reveal very low uranium concentrations from 0 003 to 0 03 g l and uranium activity ratios slightly greater than unity from 1 06 to 1 62 reducing conditions within the aquifers are responsible for the low uranium concentrations the uranium activity ratios observed are well below those calculated using theoretical considerations of alpha particle recoil effects this can be explained by interference with alpha recoil nuclides entering the liquid phase as a result of quartz overgrowths on sand grains and high temperature re equilibration that tends to minimize the effects of the alpha recoil process the fact that the uranium activity ratios of the brines are slightly greater than unity instead of the equilibrium value of 1 000 indicates that either the alpha particle recoil blocking and re equlibration effects are not complete or that another process is operative that enriches the fluid in excess 234 u by selectively removing uranium from radiation induced damage sites in the mineral sand grain matrix

experimental evidence of uraninite formation from diagenesis of uranium rich organic matter abstract this study focuses on the experimental diagenetic evolution of an uranium rich lignite from the coutras uranium deposit gironde france located in eocene sediments three samples containing 6 to 15 5 wt uranium were analysed and compared to two barren samples located outside the ore deposit in a stratigraphically equivalent unit uranium in the mineralized samples is present as uranyl carboxylic complexes dry thermal maturation was simulated in a cold seal autoclave at 150 200 250 300 and 350 c at 100 mpa for 24 h with increasing temperature uranyl carboxylic complexes decompose while uraninite forms the chemical composition of the experimentally matured barren samples when plotted in a van krevelen diagram h c vs o c parallels the natural trend of land derived type ill organic matter evolution while mineralized samples are characterized by a higher loss of hydrogen above 250 c reduction to form uraninite is directly related to the dehydrogenation of lignite the resulting uraninite has a similar unit cell edge to that of natural uraninites observed in sedimentary environments uraninite not only forms in the pore space but also replaces the lignite constituents the results demonstrate that uraninite may form during thermal evolution of uranium rich organic matter during diagenesis

reconstruction of past u migration in a sedimentary deposit coutras france implications for a radwaste repository this study is focused on ancient u mobility in unconsolidated kaolinite bearing sediments from the outcrop area of the coutras u deposit gironde france the analysis of radiation induced defects by electron paramagnetic resonance spectroscopy shows significant variations among the investigated samples and provides the paleodoses due to u at coutras the highest paleodose does not correspond to the highest u concentrations indicative of a past concentration of uranium different from the present one the paleodose gives an estimate of the equivalent u concentrations eu responsible for the defect concentration assuming an age for the kaolinites and considering extreme degrees of disequilibrium among u decay chain as uncertainties of the method the comparison between the equivalent eu and normalized present day u concentrations u norm reveals past migration of u when these two concentrations are different past occurrence of u and daughters is revealed even when this radioelement has been subsequently leached indeed surface sandy beds show a slight barely significant leaching evidence of u eu u norm in contrast several samples show u norm much greater than eu which suggests past accumulation of u younger than the sediment deposition particularly in organic rich clay layers these late enrichments may reach several hundreds ppm u isotopic constraints from the literature imply that accumulation is older than 1 ma in the organic clayey beds although the time of transfer or spatial dispersion of u cannot be specified from the methodology and the limited set of samples the quantitative analysis of radiation induced defects in clays yields intensity of past radioisotope transfers at the geological timescale it is relevant for the analysis of u mobility in sedimentary natural analogues of high level nuclear waste repositories it is also complementary to classical isotopic analysis of u and th series

hydrogeochemical modelling of an active system of uranium fixation by organic soils and sediments needle s eye scotland uranium accumulation in organic rich sediments can be closely modelled by assuming that the dominant effect of the uranium organic matter interaction is the direct or indirect reduction of uranyl compounds to form u iv minerals especially uraninite pitchblende application of this model to the needle s eye scotland site where uranium is actively accumulating in quaternary sediments demonstrates that uranium accumulation is both effective and rapid in environments involving shallow organic rich reducing horizons the period of uranium deposit formation at needle s eye is estimated to be as short as 5000 years the transport of uranium to the site of deposition by oxidizing groundwaters and the channelling of these oxidizing uraniferous groundwaters are identified as important factors involved in the rapid accumulation of uranium the regional hydrogeological model indicates that a fault in the area appears to act as a hydraulic screen for the uraniferous groundwaters on one side of the fault the quaternary sediments are well drained whilst on the other the flow of groundwater seeps out creating a major flux just at the bottom of the organic rich layers the local hydrogeological model shows that the groundwater flow is vertical in this area a third significant factor in the development of these uranium accumulations is the presence of a significant nearby source of leachable primary uranium in the case of the needle s eye site this is in the form of some thirty 185 20 ma pitchblende bearing veins

the u contents and 234u 238u activity ratios of dissolved uranium in groundwaters from some triassic sandstones in england abstract the isotopic compositions of dissolved uranium in groundwaters of age up to 36 000 a from the east midlands triassic sandstone and in saline fluids from deep geothermal boreholes in the wessex basin have been investigated groundwaters from the east midlands have u contents which lie on a normal distribution and average 0 75 g kg 1 with a standard deviation of 0 4 g kg 1 the 234 u 238 u activity ratios for the dissolved u in these groundwaters have minimum values between 3 and 4 some groundwaters have further enhancement of the 234 u 238 u activity ratio up to 7 but this is not related to groundwater age it is shown that uranium solution is primarily controlled by carbonate solution involving the cement phase of the sandstone and that the 234 u 238 u activity ratios are the results of preferential chemical etch of 234 u relative to 238 u an eh ph stability field diagram calculated for the average groundwater hco 3 contents in the aquifer shows that the uranyl carbonate complexes uo 2 co 3 2 2 and uo 2 co 3 3 4 stabilise uranium solution in the east midlands groundwaters in the wessex basin the redox conditions indicate that uranium deposition should occur and this is reflected in the very low u content of the geothermal fluids g kg 1 the residence time of these thermal waters probably exceeds 15 ma and a steady state 234 u 238 u activity ratio due to alpha recoil induced solution of 234 u should therefore have been attained the activity ratio 2 0 is very much less than the theoretical steady state ratio 10 20 for recoil processes in the interstitial fluids of the sandstone it is concluded that u in the interstitial surfaces must have been sealed against alpha recoil processes by a phase of low u content if the thermal water has evolved from groundwater similar to that in the east midlands triassic sandstone decay of excess 234 u must have occurred the time required for this decay is at least 0 25 ma if no alpha recoil solution of 234 u occurs and is 1 25 ma if an alpha recoil steady state has been attained the general implications of the study on the use of 234 u 238 u activity ratio changes for the estimation of groundwater residence times are discussed

uranium mobility in the sediment hosted uranium deposit of coutras france abstract recent mobility of u was investigated in the coutras u deposit gironde france located in lutetian sediments near the surface the coutras deposit is a belt of tabular ore bodies separated into two areas by the dronne river the jean vincent area close to the surface and the le fieu area located at a maximum depth of 100 m the immobility of th is supported by whole rock th contents which do not vary significantly with u content the present hydrological regime in the jean vincent area is characterized by oxidizing waters flowing toward the dronne river activity ratios ar of 230th 234u in rocks which range from 0 55 to 12 demonstrate recent u accumulation and leaching the 234u 238u ar range from 0 94 to 1 52 in the rocks and from 0 94 to 1 61 in the waters recent accumulation of u is favored along redox barriers where mo v se and as are also mobilized waters in the le fieu area are nearly stagnant they are reduced and exhibit a different chemical composition than waters in the jean vincent area with higher contents of ca mg na k cl hco3 po4 ra ba mn higher 234u 238u ar 1 33 4 63 and lower u content the le fieu rock samples do not show any isotopic evidence of recent leaching of u but both relative excesses and deficits of 234u are observed preferential mobility of 234u in the reduced le fieu area is interpreted according to the recoil model the results place new constraints on the model of cowart and osmond and should be useful in prospecting for tabular u deposits in reduced environments

uranium and organic matter in a paleodeltaic environment the coutras deposit gironde france the coutras uranium deposit located north of the aquitaine basin france was discovered by cogema in 1980 it is hosted by middle eocene arenaceous unconsolidated sediments at the surface the jean vincent area and down to 100 m depth the le fieu area the detrital components of the sediments are mainly quartz feldspars and granitic and metamorphic rock fragments the host sediments originated from the french massif central to the east orebodies are black tabular lenses occurring in sediments deposited in a delta plain environment where plant debris is abundant preservation of ligneous vegetation during burial established a reducing environment capable of concentrating uranium there is a good correlation between uranium total sulfur and organic carbon uranium is mainly fixed in organics as organo uranyl compounds uranium minerals detected include coffinite pitchblende and secondary hexavalent u minerals accumulation of uranium was favored by a permeable organic rich and slightly acid environment adsorption processes probably enhanced ore formation the lack of oxidized tongues may be the result of oxygen depleted uranium bearing solutions when they reached the organic rich zone the coutras uranium deposit is then a good example of a tabular type deposit which was deposited during early diagenesis

late miocene onset of the amazon river and the amazon deep sea fan evidence from the foz do amazonas basin new biostratigraphic isotopic and well log data from exploration wells on the outer continental shelf and uppermost amazon deep sea fan brazil reveal that the amazon river was initiated as a transcontinental river between 11 8 and 11 3 ma ago middle to late miocene and reached its present shape and size during the late pliocene prior to the late miocene the continental shelf was a carbonate platform that received moderate siliciclastic sediment supply from the proterozoic basement in eastern amazonia average sedimentation rates on the amazon fan show three stages of development 1 11 8 6 8 ma ago low sedimentation rates 0 05 m ka prevailed on the fan because the amazon river was not yet entrenched and some sediments were partially trapped in continental basins 2 6 8 2 4 ma ago sedimentation rates 0 3 m ka increased the river entrenched and deposition fully migrated onto the amazon fan 3 2 4 ma ago to the present very high sedimentation rates 1 22 m ka with peaks of 11 m ka prevailed on the fan and the modern amazon river developed all these paleogeographic and depositional events are closely related to andean tectonism late miocene pliocene and were exacerbated by global cooling and sea level fall during the late miocene

a comparative study of aquifer systems occurring at the parana sedimentary basin brazil u isotopes contribution the radioactivity due to 238u and 234u in three aquifer systems occurring within the parana sedimentary basin south america has been investigated uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the u mobility coefficients between 7 6 10 6 and 1 2 10 3 g cm 3 these values are also compatible with the u preference ratios relative to na k ca mg and sio2 which showed that u is never preferentially mobilized in the liquid phase during the flow occurring in cracks fissures fractures and faults of the igneous basaltic rocks experimental dissolution of diabase grains on a time scale laboratory has demonstrated that the u dissolution appeared to be a two stage process characterized by linear and second order kinetics the u dissolution rate was 8 10 16 mol m 2 s 1 that is within the range of 4 10 16 3 10 14 mol m 2 s 1 estimated for other rock types the 234u 238u activity ratio of dissolved u in solutions was higher than unity a typical result expected during the water rock interactions when preferential 234u leach from the rock surfaces takes place some u isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in sao paulo state a modeling has been also realized considering all u isotopes data obtained in bauru 35 samples serra geral 16 samples and guarani 29 samples aquifers the results indicated that the bauru aquifer waters may result from the admixture of waters from guarani 1 5 and serra geral 98 5 aquifers

uranium thorium series radionuclides in brines and reservoir rocks from two deep geothermal boreholes in the salton sea geothermal field southeastern california naturally occurring u and th series radionuclides have been analyzed in high temperature brines 300 c 25 wt dissolved solids and associated rocks from two deep geothermal wells located on the northeastern margin of the salton sea geothermal field ssgf these data are part of a study of the ssgf as a natural analog of possible radionuclide behavior near a nuclear waste repository constructed in salt beds and permit evaluation of some characteristics of water rock interaction in the ssgf rock brine concentration ratios rc dpm g rock dpm g brine were found to vary from near unity for isotopes of ra pb and rn to about 5 105 for 232th the high sorptivity of 232th is closely followed by that of 238u and 234u rc 5 104 suggesting that u is retained in the 4 oxidation state by the reducing conditions in the brines the relatively high solubility of 210pb and 212pb is attributed to formation of chloride complexes while the high ra solubility is attributed to chloride complexing a lack of suitable adsorption sites due to the high brine salinity and temperature and the reducing conditions that prevent mno2 and raso4 from forming the 228ra226ra ratios in the brines are approximately equal to those of their parents 232th230th in associated rocks indicating that ra equilibration in the brine rock system is achieved within the mean life of 228ra 8 3 years the 224ra228ra ratios in these brines are about 0 7 indicating that either 1 brine composition is not homogeneous and 224ra decays in fracture zones deficient in ra and th as the brine travels to the wellhead or 2 ra equilibration in the brine host rock system is not complete within the mean life of 224ra 5 2 days because the desorption of 224ra from the solid phase is impeded the 228ac228ra activity ratio in the ssgf brines studied is 0 1 and from this ratio the residence time of 228ac in the brine before sorption onto solid surfaces is estimated to be 70 minutes indicating the potential for rapid removal of reactive isotopes fom brines the brine is greatly enriched in 226ra 2 3 dpm g about 104 105 times that of its parent 230th while reservoir rocks are about 10 deficient in 226ra relative to 230th material balance calculations for 2226ra and 18o suggest that brines reside in the reservoir for 102 103 years that the ssgf formed 10 000 40 000 years b p and that porosity cannot be more than 20

contact zones and hydrothermal systems as analogues to repository conditions abstract radioactive waste isolation efforts in the u s a are currently focused on examining basalt tuff salt and crystalline rock as candidate rock types to encompass waste repositories as analogues to near field conditions the distributions of radio and trace elements have been examined across contacts between these rocks and dikes and stocks that have intruded them the intensive study of the stripa quartz monzonite in sweden has also offered the opportunity to observe the distribution of u and its daughters in groundwater and its relationship to u associated with fracture filling and alteration minerals investigations of intrusive contact zones to date have included 1 a tertiary stock into precambrian gneiss 2 a stock into ash flow tuff 3 a rhyodacite dike into columbia river basalt washington and 4 a kimberlite dike into salt with respect to temperature and pressure these contact zones may be considered worst case scenario analogues results indicate that there has been no appreciable migration of radioelements from the more radioactive intrusives into the less radioactive country rocks either in response to the intrusions or in the fracture controlled hydrologic systems that developed following emplacement in many cases the radioelements are locked up in accessory minerals suggesting that artificial analogues to these would make ideal waste forms emphasis should now shift to examination of active hydrothermal systems studying the distribution of key elements in water fractures and alteration minerals under pressure and temperature conditions most similar to those expected in the near field environment of a repository

processes controlling 234u and 238u isotope fractionation and helium in the groundwater of the st lawrence lowlands quebec the potential role of natural rock fracturing abstract the goal of this study is to explain the origin of 234 u 238 u fractionation in groundwater from sedimentary aquifers of the st lawrence lowlands quebec canada and its relationship with 3 he 4 he ratios to gain insight regarding the evolution of groundwater in the region 234 u 238 u activity ratios or 234 u 238 u act were measured in 23 groundwater samples from shallow quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the becancour river watershed the lowest 234 u 238 u act 1 14 0 01 was measured in ca hco 3 type freshwater from the quaternary shallower aquifer where bulk dissolution of the carbonate allows u to migrate into water with little 234 u 238 u isotopic fractionation the 234 u 238 u act increases to 6 07 0 14 in na hco 3 cl type groundwater preferential migration of 234 u into water by recoil is the underlying process responsible for this isotopic fractionation an inverse relationship between 234 u 238 u act and 3 he 4 he ratios has been observed this relationship reflects the mixing of newly recharged water with 234 u 238 u act close to the secular equilibrium and containing atmospheric tritiogenic helium and mildly mineralized older water 14 c ages of 6 6 kyrs with 234 u 238 u act of 6 07 and large amounts of radiogenic 4 he in excess of the steady state amount produced in situ the simultaneous fractionation of 234 u 238 u act and the addition of excess 4 he could be locally controlled by stress induced rock fracturing this process increases the surface area of the aquifer matrix exposed to pore water from which produced 4 he and 234 u can be released by recoil and diffusion this process would also facilitate the release of radiogenic helium at rates greater than those supported by steady state u th production in the rock consequently sources internal to the aquifers could cause the radiogenic 4 he excesses measured in groundwater

uranium series isotopes in the groundwater of the permo triassic sandstone aquifer lower mersey basin u k abstract an investigation of u and th series isotopes in rock and groundwater samples from a permo triassic sandstone aquifer of northwest england is described the groundwaters sampled range in age and composition from fresh and modern to highly saline and ancient with at least two sources of salinity highest u and th concentrations are present in the mudrock beds within the sandstone sequences the 234u 238u and 226ra 230th rock activity ratios suggest that saline waters were once much more extensive throughout the aquifer and have been flushed by several volumes of fresh groundwater since the last glaciation uranium contents and activity ratios confirm that the isotope signatures observed in most of the sampled groundwaters are not the result of simple conservative mixing relations between high u saline waters and low u fresh groundwaters but that the isotopic content of the matrix the matrix mineralogy and fabric the redox conditions the salinity and possibly the carbonate chemistry are all important petrographic studies have demonstrated the multiphase nature of the sandstones and although the isotopic signatures are consistent with the origins of the sampled water as concluded from other hydrochemical and hydrogeological data quantitative modelling of the processes involved is limited by lack of details of u bearing phases pore architecture and the chemistry of u in high ionic strength solutions however ra concentrations are controlled by sorption processes and ra is shown to be mobilised under saline conditions the mechanisms of rn release from the aquifer matrix are reviewed and a rn release factor of 0 11 is calculated this value is believed to be inappropriate as a measure of the recoil supply of the longer lived rn precursors in the u decay series

spatial distribution and geochemical baselines of major trace elements in soils of medak district andhra pradesh india regional scale variations in soil geochemistry were investigated with special reference to differences among soil groups and lithology in an area of 9 699 km2 in medak district andhra pradesh india the concentrations of 29 elements major si al fe mn mg ca na k ti p and trace as ba cd co cr cu f mo ni pb rb se sr th u v y zn zr in 878 soil samples collected 557 topsoil 321 subsoil at a sampling density of 1 site 17 km2 from 557 sites representative of all the soil types present in studied area were determined and their elemental composition are discussed the baseline levels of these elements in soils are determined over different lithological units for the identification of anomalous values relative to these for the first time geochemical maps for medak district are prepared on 1 50 000 scale and the lithogeochemical database generated provides information on the lateral and vertical distribution of elements in soil the spatial variations in the distribution of elements reflect underlying geologic characteristics box plots reveal that the concentration of most of the elements in soils were not strongly dependent on the soil group but the soil geochemistry abruptly changes with the change in the soil parent materials indicating that the distribution of elements is mostly influenced by the bedrock lithology and other natural processes acting on them for instance the concentrations of co cu fe mn ti v and zn are high in soils developed on basaltic terrain while the soils developed on granitic and gneissic terrain exhibit high elemental concentrations of k pb rb si th and y alfisols had relatively high contents of elements while entisols had lower concentrations of most of the elements the database can be used in the chemical characterisation of different geological units as well as applications in various environmental and agricultural fields the results indicate that regional geology is an important determinant of soil geochemical baselines for soil pollution assessment and further emphasizes the importance of determining background levels locally the defined baselines can be used to establish background values for future soil surveys

use of u isotopes in exploring groundwater flow and inter aquifer leakage in the south western margin of the great artesian basin and arckaringa basin central australia abstract the distribution of uranium isotopes 238u and 234u in groundwaters of the south western margin of the great artesian basin gab australia and underlying arckaringa basin were examined using groundwater samples and a sequential extraction of aquifer sediments rock weathering the geochemical environment and recoil of daughter products control the 238u and 234u isotope distributions giving rise to large spatial variations generally the shallowest aquifer j aquifer contains groundwater with higher 238u activity concentrations and 234u 238u activity ratios close to secular equilibrium however the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238u activity concentrations other locations in the j aquifer that receive little or no recharge contain higher 238u activity concentrations because uranium from localised uranium rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution the geochemical conditions of the deeper aquifers generally result in lower 238u activity concentrations in the groundwater accompanied by higher 234u 238u activity ratios the sequential extraction of aquifer sediments showed that recoil of 234u from the solid mineral phases into the groundwater rather than dissolution of or exchange with the groundwater accessible minerals in the aquifer caused enrichment of groundwater 234u 238u activity ratios in the boorthanna formation decay of 238u in uranium rich coatings on j aquifer sediments caused resistant phase 234u 238u activity ratio enrichment the groundwater 234u 238u activity ratio is dependent on groundwater residence time or flow rate depending on the flow path trajectory thus uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers however spatial heterogeneity and the lack of clear regional correlations made it difficult to identify recharge and inter aquifer leakage