isotopic composition of old ground water from lake agassiz implications for late pleistocene climate a uniform oxygen isotope value of 25 per mil was obtained from old ground water at depths of 20 to 30 meters in a thick deposit of clay in the southern part of the glacial lake agassiz basin the lake occupied parts of north dakota and southern manitoba at the end of the last glacial maximum and received water from the ice margin and the interior plains region of canada ground water from thick late pleistocene age clay deposits elsewhere a till in southern saskatchewan and a glaciolacustrine deposit in northern ontario show the same value at similar depths these sites are at about 50 n latitude span a distance of 2000 kilometers and like the lake agassiz sites have a ground water velocity of less than a few millimeters per year the value of 25 per mil is characteristic of meltwater impounded in the southern basin of lake agassiz this value corresponds to an estimated air temperature of 16 c compared with the modern temperature of 0 c for this area

origin distribution and hydrogeochemical controls on methane occurrences in shallow aquifers southwestern ontario canada abstract natural gas reservoirs in organic rich shales in the appalachian and michigan basins in the united states are currently being produced via hydraulic fracturing stratigraphically equivalent shales occur in the canadian portion of the basins in southwestern ontario with anecdotal evidence of gas shows yet there has been no commercial shale gas production to date to provide baseline data in the case of future environmental issues related to hydraulic fracturing and shale gas production such as leakage of natural gas saline water and or hydraulic fracturing fluids and to evaluate hydrogeochemical controls on natural gas accumulations in shallow groundwater in general this study investigates the origin and distribution of natural gas and brine in shallow aquifers across southwestern ontario an extensive geochemical database of major ion and trace metal chemistry and methane concentrations of 1010 groundwater samples from shallow domestic wells in bedrock and overburden aquifers throughout southwestern ontario was utilized in addition select wells n 36 were resampled for detailed dissolved gas composition 13 c of ch 4 c 2 c 3 and co 2 and d of ch 4 dissolved gases in groundwater from bedrock and overburden wells were composed primarily of ch 4 29 7 98 6 mol of total gas volume n 2 0 8 66 2 mol ar o 2 0 2 3 4 mol and co 2 0 1 2 mol ethane was detected but only in low concentrations 100 in situ saturation were found in bedrock wells completed in the upper devonian kettle point formation middle devonian hamilton group and dundee formation and in surficial aquifers overlying these organic rich shale bearing formations indicating that bedrock geology is the primary control on methane occurrences a few n 40 samples showed na cl br evidence of brine mixing with dilute groundwater however only one of these samples contained high 60 in situ saturation ch 4 the relatively low 13 c values of ch 4 89 9 to 57 3 covariance of d values of ch 4 and h 2 o positive correlation between 13 c values of ch 4 and co 2 and lack of higher chain hydrocarbons c 3 in all but one dissolved gas sample indicates that the methane in groundwater throughout the study area is primarily microbial in origin the presence or absence of alternative electron acceptors e g dissolved oxygen fe no 3 so 4 in addition to organic substrates controls the occurrence of microbial ch 4 in shallow aquifers microbial methane has likely been accumulating in the study area since at least the late pleistocene to the present as indicated by the co variance and range of d values of ch 4 314 to 263 and associated groundwater 19 to 6 d h 2 o

evidence of discharging saline formation water to the athabasca river in the oil sands mining region northern alberta this paper summarizes various lines of evidence including new geophysical and geochemical surveys indicating the discharge of naturally occurring saline formation water from cretaceous and devonian formations to the athabasca river downstream of fort mcmurray an active oil sands extraction area the following features are indicative of saline water discharge i the hydrogeological setting of the reach which is situated near the western up dip and subcropping edge of the western canada sedimentary basin ii springs and seepage along area rivers and tributaries that have been observed and reported in previous studies and iii a significant increase in dissolved solids in the river particularly chloride occurring in a downstream direction from fort mcmurray further evidence of the saline groundwater discharge was obtained from electromagnetic surveys conducted along a 125 km reach from the clearwater river to the firebag river this technique was used to map the distribution of saline water in

distribution of total dissolved solids in mcmurray formation water in the athabasca oil sands region alberta canada implications for regional hydrogeology and resource development total dissolved solids tds concentrations of 258 lower cretaceous mcmurray formation water samples in the athabasca oil sands region 54 to 58 n and 110 to 114 w were mapped using published data from recent government reports and environmental impact assessments mcmurray formation waters varied from nonsaline 240 mg l to brine 279 000 mg l with a regional trend of high salinity water approximately following the partial dissolution front of the devonian prairie evaporite formation the simplest hydrogeological explanation for the observed formation water salinity data is that devonian aquifers are locally connected to the mcmurray formation via conduits in the sub cretaceous karst system in the region overlying the partial dissolution front of the prairie evaporite formation the driving force for upward formation water flow is provided by the pleistocene glaciation events that reversed the regional devonian flow system over the past 2 m y in the athabasca region this study demonstrates that a detailed approach to hydrogeological assessment is required to elucidate tds concentrations in mcmurray formation waters at an individual lease area scale the observed heterogeneity in formation water tds and the potential for present day upward flow has implications for both mining and in situ oil sands resource development

a 40 year record of carbon 14 and tritium in the christchurch groundwater system new zealand dating of young samples with carbon 14 summary knowledge of the sources and flowpaths of water in the christchurch groundwater system will be vital to future management of the system to gain such knowledge oxygen 18 18 o tritium 3 h carbon 14 14 c and chemical concentrations have been measured on deep and shallow groundwaters since 1970 18 o measurements show that seepage from the waimakariri river is the dominant source of the groundwater early 3 h measurements in the 1970s showed non zero concentrations in the deep groundwaters but these were discounted at the time as due to at most a few percent of very young water however reinterpretation in light of the 14 c ages in this work has revealed much younger ages for the deep waters than was previously believed with average ages of 38 years in 1971 71 years in 1976 98 years in 1985 greater than 120 years in 1986 and greater than 150 years in 1993 1994 because the waimakariri river was identified as the major source of the deep groundwater the river s 14 c concentration between 1986 and 2006 was modelled by combining the records of its two carbon sources biogenic carbon and atmospheric co 2 this allowed the initial 14 c concentrations of the groundwaters to be unequivocally determined and their mean 14 c ages estimated using the same flow model as was applied to the 3 h measurements the resulting mean 14 c ages are in the range 5 1500 years the long sequence of measurements reveals that the mean ages of the deep christchurch groundwater have changed markedly during the study the pre exploitation rate of turnover of water in the system is not known but was probably quite slow by the 1970s ages in the deep system aquifers 4 and 5 had become relatively young right across christchurch with mean ages of 60 70 years indicating mainly lateral inflow of young waimakariri river water because of groundwater abstraction mean ages measured since have gradually increased showing increasing upflow of much older water from depth this water has 10 15 rainfall recharge and is sourced from the inland plains region there is now in 2006 a steep gradient in age from west to east across christchurch from 300 years to 1400 years showing that a large body of much older deeper water is stored on the seaward side of the system where the deep aquifers are blind this body will yield good quality water for many years but eventually it is likely to be replaced or bypassed by younger a few hundred years old waimakariri river dominated but surface recharge bearing water from inland

plutonic lithics in ignimbrites of taupo volcanic zone new zealand sources and conditions of crystallisation abstract plutonic rock fragments occur as rare accessory lithics within some of the ignimbrites erupted from calderas and caldera complexes in central taupo volcanic zone tvz new zealand the two main suites of plutonic lithics are 1 medium to fine grained granitoids and 2 fine grained dolerites and microdiorites the granitoids are mostly medium grained rocks with both equigranular and granophyric intergrowth textures the latter indicating rapid crystallisation at shallow crustal levels biotite is the predominant mafic phase in most granitoid samples although rare hornblende and orthopyroxene bearing granitoids also occur glass occurs in some granitoid samples from rotoiti ignimbrite indicating that these samples were incompletely crystallised prior to eruption dolerite and microdiorite fragments typically contain abundant hornblende and up to 10 vesicular interstitial glass sio2 abundances in the granitoids range between 70 3 and 77 9 they are weakly metaluminous to weakly peraluminous and show an enrichment in large ion lithophile lil elements rb k ba and a depletion in nb relative to morb similar to recent tvz rhyolitic volcanic rocks chemically and petrographically the granitoids fall into two distinct groups high sr granodiorites 120 205 ppm sr and chemically more evolved low sr monzogranites 26 65 ppm sr with an apparent compositional gap between the two eu eu anomalies and strong correlations between al2o3 cao and sr indicate that compositional variation between the two granitoid groups is dominantly controlled by plagioclase fractionation the high and low sr groups coincide with the highest and lowest sr concentrations observed in tvz rhyolites ree data and sr nd pb and o isotope ratios for granitoids are comparable to published data for tvz rhyolites and consequently they are considered to represent crystallised portions of zoned silicic magma chambers associated with quaternary tvz volcanic activity and not fragments of older pre tvz basement most granitoids are regarded as comagmatic with their host ignimbrites but those from rotoiti ignimbrite have different mineral assemblages and whole rock chemistry to the host ignimbrite these fragments appear to be incompletely crystallised portions of an earlier magma system possibly the same system that generated the matahina ignimbrite dolerites and microdiorites are geochemically similar to evolved high alumina basalts erupted from the central tvz and are considered to be intrusive equivalents

origin and geochemistry of saline spring waters in the athabasca oil sands region alberta canada abstract the geochemistry of saline spring waters in the athabasca oil sands region aosr in alberta canada discharging from devonian carbonate rocks into the athabasca and clearwater rivers was characterized for major ions trace elements dissolved gases and polycyclic aromatic hydrocarbons pahs in addition stable isotope analyses of h2o so4 dissolved inorganic carbon dic sr and ch4 were used to trace the sources of spring waters and their dissolved solutes and to identify subsurface processes affecting water chemistry the spring waters had 18o values as low as 23 5 suggesting they are composed of up to 75 laurentide glacial meltwater tritium and radiocarbon age dating results analyzed for three spring waters supported a glacial origin the high salinity of the spring waters tds 7210 51 800 mg l was due to dissolution of devonian evaporite and carbonate deposits in the subsurface spring waters were affected by bacterial dissimilatory sulfate reduction methanogenesis and methane oxidation trace elements were present in spring waters at varying concentrations with only one spring containing several predominant oil sands metals as fe mo ni se zn suggesting bitumen as a source five springs contained elements al as b fe se at concentrations exceeding water quality guidelines for the protection of aquatic life seven pahs were detected in spring waters total pah concentrations ranged from 7 3 to 273 6 ng l but most springs contained a maximum of two pahs phenanthrene and naphthalene with more pahs being detected in springs along the athabasca river this geochemical characterization of the saline groundwater discharging from the devonian carbonates underlying oil sands deposits contributes to the knowledge of baseline groundwater chemistry in the aosr which is of importance in the delineation of natural versus anthropogenic effects on regional surface water and groundwater quality

influence of till provenance on regional groundwater geochemistry abstract a regional groundwater geochemistry study was conducted in the paskapoo formation of southern alberta canada our study area focused on a region where two continental ice sheets the cordilleran and laurentide met the glacial deposits transported by these ice sheets have different bulk characteristics reflective of the bedrock of the source region of the ice recharge through these two different glacial deposits generates distinctly different water geochemistry within the underlying paskapoo formation such that bedrock aquifer acquires a geochemical signature of the immediately overlying glacial deposits through which recharge occurs oxidation of pyrite in laurentide till generates high sulphate groundwater and associated acid generation leads to enhanced mineral weathering this generates high tds high na so4 groundwater in underlying bedrock aquifers this process appears transitory where thin laurentide drift deposits are completely oxidized and have reduced capacity to generate high sulphate water the same bedrock underlying carbonate dominated cordilleran drift deposits have low tds ca hco3 groundwater

carbon isotope exchange rate of dic in karst groundwater abstract the kinetics of isotopic exchange between dissolved inorganic carbon dic of groundwater and calcite of the matrix of karst aquifers of cyrenaica libya can be deduced from 13 c and 14 c data the aquifers are mostly confined and the majority of the wells do not show any occurrence of modern recharge in 1976 1980 in fact the tritium content was below 1 tritium unit tu in most sites assuming that the isotopic exchange takes place through a first order reaction such as 14 c radioactive decay it can be shown that a linear correlation occurs between ln a and ln m e p where a is the 14 c activity m and are the 13 c contents of matrix calcite and dic respectively and e p is the 13 c enrichment in caco 3 precipitation the slope of the correlation provides the half life of the isotopic exchange process for cyrenaica karst groundwater a half life of about 11 000 years is obtained i e about double that of 14 c radioactive decay the isotopic exchange kinetics also depends on the ratio between groundwater volume and the calcite surface exposed to the exchange process thus other aquifers will show different exchange half life values the cretaceous chalk aquifers of the paris basin france and lagerdorf germany give a half life of about 4000 years much shorter than that of cyrenaica which may be due to the high porosity i e to the large surface available for the isotope exchange process the berkshire chalk aquifer uk gives a half life of about 10 000 years much higher half lives above 20 000 years are obtained for two sandy aquifers in flevoland the netherlands and texas usa which could be explained by the low caco 3 content of the aquifer matrix the highest half life value about 40 000 years is obtained in an artesian limestone aquifer in florida usa

using regional datasets of isotope geochemistry to resolve complex groundwater flow and formation connectivity in northeastern alberta canada abstract in the southern athabasca oil sands saos region located in alberta canada individual in situ oil sands operators have conducted local geochemical and isotope groundwater studies to establish baseline characteristics and to improve understanding of the connectivity of water supply and disposal formations within individual leases canada s oil sands innovation alliance cosia initiated this study to combine the data from these individual studies along with public information into a comprehensive unified dataset to evaluate conceptual models of regional groundwater flow and the degree of interaction and separation between important water supply and disposal aquifers the unified dataset comprised over 293 groundwater samples from the main water source and disposal hydrostratigraphic units and included geochemical and isotopic tracers that can be used to identify sources 18o and 2h and age of water 3h and associated solutes 14cdic 36cl as well as the sources of salinity and diagenetic processes 13cdic 34sso4 87sr 86sr 11b 37cl and 81br and dissolved organics 13cdoc the tds and stable isotope composition 18o and 2h of groundwater from several cretaceous formations were used to identify three main mixing controls i areas where locally recharged groundwater mixes with glaciogenic water were identified by lower 18o and 18o values high tds cl br and 34sso4 87sr 86sr and 37cl values consistent with dissolution of evaporites these areas were situated where vertical pathways through otherwise competent formations are likely to occur ii mixing with paleo waters characterized by high tds and higher 18o and 2h signatures indicating groundwater recharged under warmer climate periods and or evaporative enrichment were identified in the south and southwestern portions of the study area the presence of these paleo waters indicate slow moving groundwater zones with limited lateral and vertical connectivity iii areas with potential connectivity to shallow aquifers were identified by their lower tds values modern meteoric 18o and 2h signatures hco3 type waters and 34s so4 and 87sr 86sr signatures consistent with weathering of shallow aquifer material geochemical and isotopic indicators suggest that in areas where the colorado group aquitard is thin or absent there is greater connectivity between the grand rapids formation and the shallower aquifers interpretation of the new unified dataset has improved understanding of the extent that glacial recharge had on devonian aquifers and overlying cretaceous formations and identified zones with relatively stagnant groundwater flow both of which have implications for regional groundwater resource development monitoring and potential wastewater disposal

quantifying saline groundwater seepage to surface waters in the athabasca oil sands region western canadian oil sands contain over 170 billion barrels of proven unconventional petroleum reserves currently extracted at 1 8 million barrels per day by either surface mining or by in situ techniques that require subsurface injection of steam and hydrocarbon solvents natural high salinity springs are known to add water and entrained inorganic and organic constituents to the athabasca river and its tributaries in the region of ongoing bitumen production however the magnitude and synoptic distribution of these saline inputs has remained unquantified here a chloride mass balance is used to estimate saline groundwater discharge to the athabasca river from 1987 to 2010 results show that the highest saline water discharge rate to the athabasca river occurs between ft mcmurray and the peace athabasca delta supported by subcrop exposure of lower cretaceous and devonian aged formations bearing saline waters further the input of saline groundwater is found to be an important control on the chemistry of the lower athabasca river despite comprising 10 1 to 3 of the athabasca river s discharge the flux of natural saline groundwater entering the athabasca does not appear to have increased or decreased from 1987 to 2010 the origin of seep salinity is interpreted as relict subglacial meltwater that has dissolved devonian aged evaporites supported by saline na cl type waters with low 18 o 16 o and 2 h 1 h ratios relative to modern precipitation the magnitude of groundwater discharge and its impact on the athabasca river s chemistry in the area of ongoing bitumen development warrants the incorporation of natural groundwater seepages into surface water quality monitoring networks

hydrogeology of formation waters northeastern alberta basin the hydrogeological study of formation waters in the northeastern part of the alberta basin defined as the area from 55 to 58 n and from 110 to 114 w is based on information from 12 475 wells 3187 formation water analyses 2531 drill stem tests and 452 030 core plug analyses because the study area covering approximately 76 000 km2 is located at the feather edge of the basin local topography and physiographic features particularly the athabasca river system exert a strong influence on the flow of formation waters in most of the aquifers generally temperature seems to be the main controlling factor on salinity distributions the salinity of formation waters increases in the vicinity of evaporitic beds and decreases close to the surface beca se of mixing with fresh meteoric water introduced through local flow systems the lower and middle devonian pre prairie aquifer systems beneath the regionally extensive prairie aquiclude are characterized by regional topographically driven flow updip to the northeast this updip flow is opposed by buoyancy forces caused by salinity increase with temperature downdip to the southwest the post prairie devonian aquifers are characterized by transitional flow regimes because of erosion at the sub cretaceous unconformity and outcrop at the athabasca river local physiographic influences are superimposed on basin scale regional flow in these aquifers hydraulic communication between the beaverhill lake cooking lake and grosmont aquifers is inferred in places caused by cooking lake reefs penetrating the intervening shales of the lower ireton aquitard finally the retaceous aquifers all can be described as having local flow regime characteristics with no buoyancy effects as a result of recharge in topographically high areas and discharge in low regions along the valleys of the athabasca river system the flow of formation waters in northeastern alberta played an important role in the formation of the huge athabasca oil sands deposits hydrocarbons that migrated into the area from the west were trapped into local reservoirs and biodegraded and washed by fresh meteoric water introduced by local flow systems environmentally the subsurface hydrogeology in the area imposes specific constraints on waste disposal in deep formations mostly because of the absence of a thick continuous regional aquitard and because most aquifers subcrop at shallow depth or crop out and discharge along the valleys of the athabasca river system and at the basin edge

deducing the distribution of terminal electron accepting processes in hydrologically diverse groundwater systems the distribution of microbially mediated terminal electron accepting processes teaps was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor nitrate sulfate consumption intermediate product hydrogen h sub 2 concentrations and final product ferrous ion sulfide and methane production in each hydrologic system a determination of predominant teaps could be arrived at but the level of confidence appropriate for each determination differed in a portion of the lacustrine aquifer of the san joaquin valley for example all three indicators sulfate concentrations decreasing h sub 2 concentrations in the 1 2 nmol range and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant teap leading to a high degree of confidence in the determination in portions of the floridan aquifer and a petroleum hydrocarbon contaminated aquifer sulfate reduction and methanogenesis are indicated by production of sulfide and methane and hydrogen concentrations in the 1 4 nmol and 5 14 nmol range respectively however because electron acceptor consumption could not be documented in these systems less confidence is warranted in the teap determination in the black creek aquifer no pattern of sulfate consumption and sulfide production were observed but h sub 2 concentrations indicated sulfate reduction as the predominant teap in this case more where just a single line of evidence is available the least confidence in the teap diagnosis is justified because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes it provides a better description of predominant redox processes in groundwater systems than more traditional eh based methods less

brine inclusions in halite and the origin of the middle devonian prairie evaporites of western canada abstract brines were extracted from fluid inclusions in lower salt halite of the middle devonian prairie formation in saskatchewan canada the brines were analyzed by ion chromatography and were found to be of the na k mg ca cl type they do not fall along a simple evaporation trend brines from clear diagenetic halite are significantly lower in na and higher in mg2 ca2 and cl than brines from cloudy subaqueously formed halite with chevron structures the isotopic composition of strontium and sulfur in anhydrite associated with the halites was found to be the same as that of middle devonian seawater the composition of the inclusion brines can be derived from that of modern seawater by evaporation extensive dolomitization of limestone a d albitization of clay minerals other evolution paths are however also feasible and it is impossible to rule out effects due to the addition of nonmarine waters hydrothermal solutions surface runoff and groundwater or dissolutional recycling of existing evaporites within the prairie evaporite basin our analyses and published data on brine inclusions in halite from a number of phanerozoic evaporite deposits show that the na k mg ca cl type brine is more common than the na k mg cl so4 type which is expected from evaporation of modern seawater

regional hydrogeochemistry of the carbonate rock aquifer southern manitoba middle ordovician to middle devonian carbonates in the manitoba lowlands form an extensive aquifer system along the eastern edge of the williston basin the aquifer is divided into fresh and saline portions by a series of topographic lows defined by major river systems and lakes that create a north south trending hydraulic divide east of this divide ca mg hco3 fresh waters are derived by active modern day recharge focused in the sandilands and interlake regions stable isotope and geochemical data indicate that na cl saline waters west of the divide are a mixture of original basin brines and glacial melt water pushed into the basin during pleistocene glaciation high na cl and cl br ratios are consistent with significant salt dissolution by glacial melt water

shallow groundwater surface water interactions in pond peatland complexes along a boreal plains topographic gradient shallow pond peatland complexes are important water resources and waterbird habitat on the boreal plains of canada and are potentially threatened by accelerated resource development we examined two shallow pond peatland complexes located in contrasting topographic positions within a clay rich till region one on a moraine and one on a lowland clay plain to evaluate the influence of landscape position on wetland groundwater surface water interactions hydrologic function and potential response to disturbance hydrometric and geochemical measurements indicated that precipitation and evaporation dominated the annual water balance of both ponds forested mineral uplands adjacent to the pond peatland complexes contributed no runoff inputs small recharge rates 5 mm year 1 from the ponds through low permeable clay to the underlying aquifer were measured at both topographic locations shallow groundwater fluxes to from the pond were controlled by water storage in and exchange with the adjacent riparian peatlands shallow groundwater fluxes may have contributed as much as 23 of inputs and outputs and influenced pond chemistry and permanence shallow groundwater exchange between the pond and adjacent peatlands varied seasonally and differed between the moraine and lowland complex groundwater flow reversals occurred around the entire perimeter of the moraine pond recharge from the moraine pond to the peatland during dry periods was off set by discharge to the pond from the peatland during wet periods in contrast shallow groundwater flow through conditions were observed at the lowland pond for most of the study however during a high rainfall event a groundwater flow reversal within the outflow peatland initiated discharge back into the pond these results suggest that the hydrologic regimes of some pond peatland complexes in clay rich till within the boreal plains will be more sensitive to local scale disturbances that impact flow dynamics and storage of near shore peatlands rather than larger scale disturbances of mineral upland regions

combining hydrodynamics hydrochemistry and environmental isotopes to understand the hydrogeological functioning of evaporite karst springs an example from southern spain abstract this work adopts a multicriteria approach combining diverse karst hydrogeology techniques to investigate the functioning of evaporite karst systems which are normally less studied due to the poor quality of their water resources the applicability of using several methods was also verified in view of previous experience at a pilot site within southern spain the natural responses of the main discharge point of the system of study lower anzur spring were controlled by continuous monitoring of the discharge rate water temperature and electrical conductivity water samples were collected for chemical analysis and for the determination of intrinsic fluorescence water stable isotopes 18o 2h and tritium 3h concentrations physico chemical data were statistically examined applying principal component analysis pca and trend analysis tests mann kendall and sen s slope the system shows a clear karstic functioning highly dependent on concentrated recharge and influenced by a limited drainage capacity of the conduit network the piston flow effects at the beginning of floods indicate a contribution to the drainage of deep ascending flows through the saturated zone subsequent drops in temperature and mineralization values in the water drained by the spring as well as a recent infiltration deduced from the signature of intrinsic fluorescence and stable isotopes point to a good hydrogeological connection from the recharge areas to the spring later restoration of the initial values of mineralization in a much shorter time than those of temperature reveals a faster geochemical evolution of the recently infiltrated groundwater which may be a distinctive trait of evaporite karst aquifers lastly the high solute content of the spring water in depletion conditions with ascending trends of mineralization and temperature observed during several dry years as a consequence of lower recharge contribution together with the tritium activity of selected samples suggest the existence of an old component partly responsible for the spring base flow thus groundwater would be linked to gravity driven regional flows but also to recent conduit flows all the results obtained led us to devise a hydrogeological conceptual model to precisely reflect the functioning of the studied system the results presented here demonstrate the advantages of using diverse techniques when investigating evaporite karst aquifers

origin and hydrogeological setting of saline groundwater discharges to the athabasca river geochemical and isotopic characterization of the hyporheic zone abstract identifying impacts of oil sands development on aquatic ecosystems requires understanding of the natural background water quality in the athabasca oil sands region of alberta this is challenging because the athabasca river is incised directly into bitumen saturated sands of the mcmurray formation and other saline cretaceous and devonian formations this study compares the geochemical and isotopic composition of porewater sampled from the alluvial sediment beneath the athabasca river with regional groundwater data to identify the geological origin of these saline groundwaters and improve characterization of natural background sources of solutes entering the athabasca river terrain conductivity surveys conducted along the athabasca river were used to identify areas with evidence of saline groundwater discharge porewater samples were obtained from the alluvial sediment using drive point piezometers installed between 1 and 3 m below the water sediment interface and were analyzed for 18o 2h 34s so4 18o so4 87sr 86sr 13c dic 13c doc 3h and 14c the porewater in the alluvial sediment showed variable degrees of mixing with the overlying athabasca river water but the geochemical and isotopic composition in zones 1 3 and 5 are consistent with discharge of saline groundwater from cretaceous or devonian units the low percentages of modern carbon and 18o 2h 34s so4 18o so4 and 87sr 86sr signatures in the deepest porewater samples from zones 1 3 and 5 indicate glaciogenic water with high total dissolved solids originating from devonian sourced solutes theses saline groundwater discharge zones occur where higher horizontal hydraulic gradients coincide with areas of higher salinity in the adjacent cretaceous and devonian aquifers and areas with vertical connectivity with underlying devonian aquifers the results of this study demonstrate the influence of groundwater surface water interactions and saline bedrock formation water discharge to water quality along some reaches of the athabasca river which need to be considered in monitoring and water management strategies

influence of saline groundwater discharge on river water chemistry in the athabasca oil sands region a chloride stable isotope and mass balance approach abstract a chloride mass and stable isotope 37 cl balance approach was employed to calculate the effect of saline groundwater discharge into the athabasca and clearwater rivers in the athabasca oil sands region aosr in north eastern alberta canada saline groundwater affected by halite carbonate and anhydrite dissolution discharges na cl type water with total dissolved solids tds up to 51 700 mg l from exposed devonian and cretaceous units in the river valleys in this area in this study nine springs discharging groundwater with a median cl concentration of 9800 mg l were sampled and chloride stable isotope ratios were determined with 37 cl values ranging from 0 2 to 1 0 in contrast river waters had historical monthly median cl concentrations between 5 9 and 49 5 mg l and 37 cl values between 2 2 and 1 4 the discharge rate of saline groundwater was calculated to be 100 20 l s into the clearwater river and 134 68 l s into the athabasca river the chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions metals and pahs in the athabasca and clearwater rivers overall saline groundwater contributed less than 0 2 of river discharge but 0 04 39 of major ion concentrations in the rivers with highest contributions under winter low flow conditions in the clearwater river saline groundwater contributed 23 39 of average monthly cl flux and 18 32 of average monthly na flux for the same major ion fluxes in the athabasca river saline groundwater contributed 12 18 and 6 12 respectively the influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible contributing less than 1 of river fluxes of cu ni pb and zn similarly the influence on mass flux of pahs in the rivers was found to be negligible

reversal of the regional scale flow system of the williston basin in response to pleistocene glaciation low 18o values of formation waters collapse structures related to salt dissolution hydrodynamic blowout structures and biodegradation of oils all suggest a significant influx of fresh water into the williston basin along the outcrop belt in southern and central manitoba during pleistocene glaciation the thickness of the continental ice sheet over manitoba would have provided sufficient potentiometric drive to reverse the regional scale flow system of the williston basin the dynamic nature of the flow system suggests that modern day pressure distributions may not be good proxies for ancient petroleum migration pathways as is commonly assumed

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

the interglacial glacial cycle and geochemical evolution of canadian and fennoscandian shield groundwaters abstract results from cryogenic column experiments are compared with the geochemical data collected in the canadian and fennoscandian shields over the past 25 years to investigate the relative influence of the glacial interglacial cycle specifically the impact of continental glaciers permafrost and methane hydrate on the evolution of groundwater from crystalline shield environments several different geochemical indicators of freezing processes either glacial or permafrost related were utilized comparisons of na cl and br cl ratios 18 o and 2 h values and 18 o values and cl concentration during freezing fluids with different dominant cations follow distinctly different linear trends when na cl and br cl ratios are compared significantly none of the freezing trends follows the trend hypothesized by herut et al 1990 for the evolution of seawater chemistry during freezing intrusion of glacial meltwater and in situ freezing i e permafrost formation result in a similar end member when comparing 18 o values and cl concentration the geochemical influence of a freezing process on fresh brackish and some saline fluids was identified at some but not all canadian shield sites regardless of site location with respect to modern day permafrost appreciably physical and geochemical data do not support the formation of brines through any freezing process in the canadian and fennoscandian shields as hypothesized by starinsky and katz 2003 rather on all diagnostic freezing plots brines are an end member indicating a different evolutionary pathway significant depletions in 18 o with respect to modern precipitation an indication of either glacial meltwater or a freezing process were identified at depths of up to 1 km at some sites in the canadian shield and to shallower depths in the fennoscandian shield the potential of this fluid to reach such depths could be attributable to artificial gradients and mixing glacial recharge permafrost or paleo permafrost formation or methane hydrate or paleo methane hydrate formation at most locations it was not possible to distinguish between the different scenarios using the current geochemical database

subglacial recharge into the western canada sedimentary basin impact of pleistocene glaciation on basin hydrodynamics brine springs discharging from devonian carbonates of the western canada sedimentary basin have distinct water chemistry from brines in laterally equivalent units deeper in the basin stable isotope data suggest that the brine springs originated as pleistocene meltwater these waters are interpreted to originate as an influx of subglacial meltwater related to a reversal of the basin scale flow system caused by the overriding ice sheet esker distribution shows a notable relationship between shield and sedimentary rocks an integrated sedimentary basin ice sheet model supports the interpretation that high permeability carbonate units acted as preferential subglacial drains that in turn affected esker development the fluid flow history of the western canada sedimentary basin is characterized by back and forth movement through geological time in response to changing boundary conditions modern day flow systems may not then be indicative of historic movement of economic fluids through the basin

testing models for the development of spiral shaped inclusion trails in garnet porphyroblasts to rotate or not to rotate that is the question the formation of spiral shaped inclusion trails ssits is problematical and the two viable models for their formation involve opposite shear senses along the foliation in which the porphyroblasts are growing one model argues for porphyroblast rotation with respect to a geographically fixed reference frame whereas the other argues for no such porphyroblast rotation but instead rotation of the matrix foliation around the porphyroblast thus porphyroblasts with ssits cannot be used as shear sense indicators until it is conclusively determined which model best explains them any successful model must explain features associated with ssits including 1 foliation truncation zones 2 smoothly curving ssits 3 millipede microstructure 4 total inclusion trail curvature in median sections 5 porphyroblasts with ssits that have grown together 6 evidence for relative porphyroblast displacements 7 shear sense indicators inside and outside porphyroblasts 8 crenulations associated with porphyroblasts and 9 geometries in sections subparallel to spiral axes axes of rotation a detailed study of these features suggests that most if not all can be explained by both the rotational and non rotational models in spite of these models involving diametrically opposed movement senses therefore geometrical analysis of individual porphyroblast microstructures may not determine which model best explains ssits until the kinematics required to form these microstructures are better understood in particular the sense of shear along a developing crenulation cleavage specific tests for determining the shear sense along crenulation cleavages are proposed and results of such tests may conclusively resolve the debate over how ssits form

cryogenic formation of brine and sedimentary mirabilite in submergent coastal lake basins canadian arctic abstract two informally named basins mirabilite basins 1 and 2 along a submergent coastline on banks island canadian arctic archipelago host up to 1 m thick accumulations of mirabilite na 2 so 4 10h 2 o underlying stratified water bodies with basal anoxic brines unlike isostatically uplifting coastlines that trap seawater in coastal basins these basins formed from freshwater lakes that were transgressed by seawater the depth of the sill that separates the basins from the sea is shallow 1 15 m such that seasonal sea ice formation down to 1 6 m isolates the basins from open water exchange through the winter freezing of seawater excludes salts generating dense brines that sink to the basin bottom progressive freezing increases salinity of residual brines to the point of mirabilite saturation and as a result sedimentary deposits of mirabilite accumulate on the basin floors brine formation also leads to density stratification and bottom water anoxia we propose a model whereby summer melt of the ice cover forms a temporary freshwater lens and rather than mixing with the underlying brines it is exchanged with seawater once the ice plug that separates the basins from the open sea melts this permits progressive brine development and density stratification within the basins

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

molecular nitrogen in natural gas accumulations generation from sedimentary organic matter at high temperatures the occurrence of natural gas accumulations with high percentages up to 100 of molecular nitrogen in various hydrocarbon provinces represents a largely unresolved problem and a serious exploration risk in this context a geochemical and basin modeling study was performed to evaluate the potential of sedimentary organic matter to generate molecular nitrogen the masses of nitrogen present in coals if converted into molecular nitrogen are sufficient to fill commercial gas reservoirs a calculation for gas accumulations in northern germany where percentages of molecular nitrogen range from less than 5 to greater than 90 reveals that the molecular nitrogen generated in underlying coal bearing strata is sufficient to account for the nitrogen gas even in the largest fi lds in addition much of the total nitrogen in clay rich rock types such as shales and mudstones is fixed in sedimentary organic matter and may add to the nitrogen generation capacity of the coals a kinetic interpretation of the nitrogen and methane generation characteristics of humic coals during laboratory pyrolysis indicates that nitrogen is generated from organic matter in sedimentary basins at higher temperatures than methane minimum temperatures for preferential nitrogen generation are in excess of 300 c for extremely low heating rates or isothermal conditions lasting over 300 m y thus nitrogen rich gases are mainly formed in the final stage of gas generation when sedimentary rocks grade into metamorphic rocks applications of the kinetic parameters for the generation of nitrogen and methane from coaly organic matter in carboniferous sedimentary rocks are presented for part of the northwest german basin in this area immense volumes of the methane rich gas gener ted during the late paleozoic and mesozoic were lost to the atmosphere the present gas composition mainly reflects the latest cenozoic gas generation this cenozoic gas is nitrogen rich where the carboniferous source rock sequences are highly mature and deeply buried

multi textured garnets from a single growth event an example from northern norway textural relationships between porphyroblasts of biotite and garnet in metasediments in the nordkinn peninsula area of the finnmarkian caledonides of north norway are apparently complex there is evidence for two textural zones in both mineral phases and superficially the development of these appears to have overlapped at least in part in time and space this apparently complex porphyroblast growth history can be considerably simplified if only one period of garnet growth occurred and if different inclusion fabrics developed where garnet replaced biotite porphyroblasts and where it overgrew the matrix foliation the possibility that porphyroblasts with textural evidence for multiphase growth histories actually grew during a single crystallization event is of importance in the interpretation and elucidation of tectonometamorphic relationships