evidence of cfc degradation in groundwater under pyrite oxidizing conditions summary a detailed local scale monitoring network was used to assess cfc distribution in an unconfined sand aquifer in southwestern ontario where the zone of 1 5 year old groundwater was known with certainty because of prior use of a bromide tracer groundwater 5 years old was confined to an aerobic zone at 5 m depth and had cfc concentrations consistent with modern atmospheric mixing ratios at recharge temperatures of 7 11 c as was observed in the 3 m thick vadose zone at the site at depths below 6 m the groundwater became progressively more reducing however with a denitrifying horizon at 6 7 m depth and a mn and fe reducing zone below 7 m depth in the anaerobic zone 3 h 3 he ratios indicated that groundwater age continued to increase uniformly with depth to a maximum value of 27 years at 13 m depth cfc concentrations however decreased abruptly within the denitrifying zone leading to substantial age overestimation compared to the 3 h 3 he ages noble gas data indicated that the apparent cfc mass loss was not likely the result of gas stripping from possible bubble formation thus cfc degradation was indicated in the anoxic zone the field data are consistent with first order degradation rates of 0 3 yr 1 for cfc 12 0 7 yr 1 for cfc 11 and 1 6 yr 1 for cfc 113 cfc attenuation at this site coincides with a zone where reduced s pyrite is actively oxidized by no 3 and dissolved oxygen do similar behavior has been observed at other sites tesoriero a j liebscher h cox s e 2000 mechanism and rate of denitrification in an agricultural watershed electron and mass balance along groundwater flow path water resour res 36 6 1545 1559 hinsby k hojberg a l engesgaard p jensen k h larsen f plummer l n busenberg e accepted for publication transport and degradation of chlorofluorocarbons cfcs in a pyritic aquifer rabis creek denmark water resour res further demonstrating that the use of cfcs for age dating anaerobic groundwater should be approached with caution particularly if the sediment contains pyrite

archean rapakivi granite anorthosite rhyolite complex in the witwatersrand basin hinterland southern africa the gaborone granite suite and the kanye formation formed during a single magmatic event in the late archean evolution of the kaapvaal craton southern africa and may be the oldest rapakivi granite anorthosite rhyolite suite in the world the gaborone granite suite underlies an area of 6000 km2 in the northwestern part of the craton and comprises a type rapakivi granite leucogranite granophyric microgranite and minor anorthosite it is partly surrounded by the kanye formation a 1000 m thick pile of pyroclastic and flow banded rhyolitic lava precise u pb dating of granitic and granophyric components of the gaborone suite and rhyolite of the kanye formation shows that all three rock types are the same age within error 2783 2785 ma emplaced in the source area during upper witwatersrand supergroup sedimentation the gaborone kanye event has important implications for the tectonic and magmatic evolution of the northern kaapvaal craton and possibly also played an important role in the development of the adjacent auriferous sediments

tectonics of the kola collision suture and adjacent archaean and early proterozoic terrains in the northeastern region of the baltic shield as preparation for the deep seismic and other geophysical experiments along the polar profile which transects the granulite belt and the kola collision suture structural field work has been performed in northernmost finland and norway and published geological information including data from the neighbouring soviet territory of the kola peninsula have been compiled and reinterpreted based on these studies and a classification according to crustal and structural ages the northeastern region of the baltic shield is divided into six major tectonic units these units are separated and outlined by important low angle ductile shear or thrust zones of late archaean to early proterozoic age the lateral extension of these units into soviet territory and their involvement in large scale crustal deformation structures are described using the view down the plunge method a generalised tectonic cross section that predicts the crustal structures along the polar profile is compiled and the structures around the kola deep drill hole are reinterpreted the kola suture belt through parts of which the kola deep bore hole has been drilled is considered to represent a ca 1900 ma old arc continent and continent continent collision suture it divides the northeastern shield region into two major crustal compartments a northern compartment comprising the murmansk and sorvaranger units and a southern compartment including the inari unit the granulite belt and the tanaelv belt as well as the more southernly situated south lapland karelia craton of the karelian province of the svecokarelian fold belt the kola suture belt is outlined by a 2 40 km wide and ca 500 km long crustal belt composed of 1 1 early proterozoic ca 2400 2000 ma old metavolcanic and metasedimentary sequences which originally formed part of the attenuated margin of the northern archaean compartment and 2 2 the remains of a ca 2000 1900 ma old predominantly andesitic island arc terrain this island arc terrain was built up above a sw plunging subduction zone initiated ca 2000 ma ago in the southern part of a newly formed oceanic domain the kola ocean due to continued subduction and complete consumption of this ocean the northern passive margin deposits and the island arc terrain were brought into tectonic juxtaposition and during the final arc continent and continent continent collision they were overthrusted onto the northern archaean continent along its southern boundary the kola suture belt is tectonically overlain by the archaean rocks of the inari unit this unit was derived from a microcontinent split from the southern compartment the depositional basin of the protoliths of the granulite belt being formed to the south of the microcontinent the inari microcontinent appears to have wedged out towards the southeast as the continuation of the granulite belt north of the white sea is in direct tectonic contact with the kola suture belt the granulite belt is composed of high grade paragneisses and minor amounts of meta igneous rocks the paragneisses formed from thick turbidite and mass flow deposits lain down in a back arc basin south of the inari microcontinent a thermal anomaly beneath the partly oceanic basement of the back arc basin is believed to have contributed to the ca 2000 1900 ma old granulite facies metamorphism of the granulite assemblages granulite facies conditions still prevailed when the inari microcontinent overrode the granulites and when the granulite belt as such was formed and was overthrusted for at least 100 km towards the southwest in conjunction with the latter event the rocks of the basement of the basin also became involved in thrust movements these now form the tanaelv belt which shows gradational tectonic contacts towards underlying cover and basement rocks of the south lapland karelia craton although not all parts of this craton were affected by the svecokarelian deformation it is considered to belong to the karelian province of the svecokarelian fold belt a ca 1900 1800 ma old episode of wrench faulting and the intrusion of 1790 1770 ma old post kinematic granites concluded the svecokarelian evolution of the northeastern shield region

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

sequence stratigraphy and plate tectonic significance of the transvaal succession of southern africa and its equivalent in western australia the transvaal succession in the northeastern part of the kaapvaal province of southern africa is the erosional remnant of four 2 7 to 2 1 ga unconformity bounded stratigraphic units or sequences each of which is 102 to 103 m thick and spans 107 to 108 years three of these phanerozoic like cratonic sequences occur in the western part of the kaapvaal province and in the pilbara province of western australia thus the two provinces once were part of the same continent vaalbara the stratigraphically lowest sequence historically assigned to the transvaal succession is part of the ventersdorp supergroup in kaapvaal and the upper part of the fortesque group in pilbara it consists predominantly of arkosic sandstone and basaltic andesite it probably is 2687 2 ma the second sequence contains the quartz arenites dolomites and banded iron formations of the transvaal and griqualand west successions in the kaapvaal and the hamersley group in the pilbara the span of ages 2684 6 to 2432 31 ma lithologies and geographic extent of this sequence imply that the limpopo orogeny which welded the zimbabwe province to vaalbara is 2 47 ga not 2 67 0 05 ga the third sequence the pretoria and postmasburg groups in the kaapvaal and the lower part of the wyloo group in the pilbara probably is the clastic wedge generated by the limpopo orogeny the fourth sequence dominated by the felsites of the rooiberg group is restricted to northeastern kaapvaal sequence stratigraphy lithostratigraphy and lithofacies indicate that the pilbara rifted from the southern edge of western kaapvaal the penge iron formation in northeastern kaapvaal the asbesheuwels iron formation in southwestern kaapvaal and the brockman iron formation in the pilbara are the same formation in which cyclothemic units 0 6 to 15 0 m thick extended 1200 km

paleomagnetism of the late archean nyanzian system western kenya abstract the nyanzian system lavas of western kenya are believed to be the oldest rocks of the tanzanian craton intrusive age relationships suggest an age 2850 ma although direct attempts at dating the nyanzian have produced disparate results our study involves a suite of samples collected from the nyanzian basalts pillow basalts andesites and rhyolites from sixteen sites in western kenya these rocks yield a tilt corrected paleomagnetic pole at 14 n 150 e k 59 dp 5 dm 7 this pole is constrained to be older than the first d1 deformation 2472 30 ma by positive fold conglomerate and reversal tests analysis of the paleomagnetic data base for three african cratonic nuclei tanzanian kaapvaal zimbabwe and west africa for the time period from 2 0 ga to 3 0 ga demonstrates a paucity of well dated poles although there are several poles from the kaapvaal zimbabwe and tanzanian cratons which allow spot readings of their relative positions we demonstrate based on these data that the kaapvaal zimbabwe and tanzanian cratons were drifting independently at 2875 ma 2700 ma and 2450 ma this independent motion of the tanzanian and kaapvaal zimbabwe cratons indicates that previously proposed models involving african cratonic coherence can no longer be considered valid for the time period from 2850 to 2500 ma

nitrate reduction in an unconfined sandy aquifer water chemistry reduction processes and geochemical modeling nitrate distribution and reduction processes were investigated in an unconfined sandy aquifer of quaternary age ground water chemistry was studied in a series of eight multilevel samplers along a flow line deriving water from both arable and forested land results show that plumes of nitrate contaminated groundwater emanate from the agricultural areas and spread through the aquifer the aquifer can be subdivided into an upper 10 to 15 m thick oxic zone that contains o2 and no3 and a lower anoxic zone characterized by fe2 rich waters the redox boundary is very sharp which suggests that reduction processes of o2 and no3 occur at rates that are fast compared to the rate of downward water transport nitrate contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area the persistence of the high content of total dissolved ions in the no3 free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place nitrate is apparently reduced to n2 because both nitrite and ammonia are absent or found at very low concentrations possible electron donors in the reduced zone of the aquifer are organic matter present as reworked brown coal fragments from the underlying miocene and small amounts of pyrite at an average concentration of 3 6 mmol kg electron balances across the redoxcline based on concentrations of o2 no3 so42 and total inorganic carbon tic indicate that pyrite is by far the dominant electron donor even though organic matter is much more abundant groundwater transport and chemical reactions were modeled using the code phreeqm which combines a chemical equilibrium model with a one dimensional mixing cell transport model only the vertical component of the water transport was modeled since in contrast to rates along flow lines the vertical rates are close to constant as required by the one dimensional model average vertical transport rates of water in the saturated zone were obtained by tritium dating the modeling process is a two step procedure first the sediment column is initialized with natural water containing only oxygen as electron acceptor and subsequently agricultural waters containing both oxygen and nitrate are fed into the column the nitrate concentration of agricultural waters entering the saturated zone varies with time and an input function was therefore constructed by linear mixing of natural waters and agricultural waters this input function was fed into the column initialized with natural water and the model run forward in time to the year 1988 where field data are available comparison with field data shows that the variation in groundwater chemistry is well described by the model when reduction of oxygen and reduction of nitrate by pyrite oxidation are the only redox reactions occurring finally predictions are made for the distribution of water chemistry in the year 2003 downward progression of the redoxcline is accelerated by a factor of five due to nitrate pollution of the aquifer but absolute rates remain small of the order of a few centimeters per year the controlling factor for nitrate migration through the aquifer once it has reached the anoxic zone is the concentration and distribution of pyrite in the sediments

palaeomagnetic and rock magnetic study of a deeply exposed continental section in the charnockite belt of southern india implications to crustal magnetisation and palaeoproterozoic continental nucleii abstract this study has investigated palaeomagnetism and magnetic properties of a tract of continental basement in south india metamorphosed to granulite facies close to the archaean proterozoic boundary 2600 ma at former depths of 20 35 km the metamorphism is characterised by extensive development of charnockite produced by flushing of co2 rich fluids through older crust rock magnetic studies thermomagnetic high and low temperature susceptibility hysteresis and irm show that very low ti metamorphic magnetite is the ubiquitous ferromagnet in all rock types it has predominantly multidomain characteristics but is of high magnetic stability probably due to exsolution precipitation and microfracture filling producing anisotropic grain shapes magnetic susceptibility shows little increase with temperature falling to zero at 550 c implying that induced magnetisation drops to a weak paramagnetic effect near this isotherm susceptibilities and intensities of magnetisation increase from amphibolite to granulite facies and by an order of magnitude within charnockites in the lower dehydrated crust induced magnetisations are able to explain 50 of observed magnetic anomalies of deep origin intensities of magnetisation and qn values are high especially in charnockite where metasomatism has resulted in new magnetite formation and it is concluded this facies is able to explain observed magnetic anomalies provided that viscous remnant magnetisation is enhanced at depth to contribute the remaining magnetisation the magnitude of anisotropy of magnetic susceptibility ams is also increased by charnockite formation as are degrees of lineation and foliation however directions of ams in these anhydrous rocks are essentially random and reflect the static nature of the charnockite metasomatism no appreciable phanerozoic overprinting is evident in this terrane and the dominant feature of the palaeomagnetic record is a west to north shallow swathe of component directions with a minor antiparallel sequence between means summarised by a1 d i 280 8 a2 d i 319 11 and a3 d i 1 10 this swathe is interpreted as an uplift related cooling acquisition following charnockite formation at 2600 ma and a remanence age of 2600 2400 ma is implied by the absence of most of the swathe in early palaeoproterozoic and younger dyke swarms cutting the region a second group of component directions b mean d i 238 87 is similar to magnetisations found in dykes linked to an age of 2370 ma and interpreted as somewhat younger than the a swathe we argue that the entire magnetic record was acquired before final basement uplift prior to 2000 1800 ma collective late archaean early proterozoic palaeopoles from india define a low to high latitude movement of the shield at 2600 2300 ma which is replicated in contemporaneous results from the other ancient gondwana nucleii of southern africa and australia the cratonic nucleii of these three shields have the oldest laterally extensive supracrustal covers and comprise the core of the protocontinent of ur the 2900 2200 ma palaeopoles are consistent with close proximities and subsequent movements between them were apparently limited because continental proximities but not configurations were similar within the palaeozoic supercontinent of gondwana

characterization of suspended particles collected in groundwater under natural gradient flow conditions microscale eulerian variations in the flux mineralogical composition and size of suspended particles have been found in a contaminated sandy aquifer under natural gradient flow conditions during an 8 month study period particle variability has been detected along a 16 m saturated section of the aquifer at a scale of centimeters and meters in the vertical and horizontal dimensions respectively the average concentration of particles in groundwater varied between 1 and 40 mg l but high concentrations of up to 5000 mg l were determined in specific 3 cm vertical intervals of the aquifer the particles were primarily composed of caco3 11 57 quartz 7 39 and clays 8 43 most of the particles were within the 140 3000 nm size range with size modes varying from 310 to 660 nm the large amounts of suspended particles are considered to be related to high inputs of dissolved organic carbon into groundwater from sewage effluents which have been used for agricultural irrigation since the early 1960s as a result of organic matter biodegradation in the saturated zone anoxic conditions developed and the pco2 content of groundwater increased dramatically pcaco2 10 1 8 to 10 1 3 atm it is postulated that part of the carbonate cement of the rocks dissolved and detrital caco3 quartz and clay were released as colloidal particles part of the clay particles could have also been transported through the unsaturated zone into groundwater after mobilization from surface layers as a result of the intermittent input of water of different chemical quality in the prevailing anoxic conditions of groundwater at the study site dissolved oxygen concentrations of 1 mg l colloidal stability is enhanced by organic matter coating of particles

migration of contaminants in groundwater at a landfill a case study 2 groundwater monitoring devices abstract six types of devices for groundwater monitoring were used on an experimental basis in the investigation of the plume of contamination in the unconfined sandy aquifer at the borden landfill these include standpipe piezometers water table standpipes an auger head sampler suction type and positive displacement type multilevel point samplers and bundle piezometers with the exception of the first two each of these devices provides a means of obtaining vertical sample profiles of groundwater from a single borehole the auger head sampler which is a device that is attached to the cutting head of conventional continuous flight hollow stem augers yields samples from relatively undisturbed aquifer zones as the augers are advanced downward in the borehole from one depth of sampling to another this method is a rapid means of aquiring water quality profiles for mapping the distribution of a contaminant plume the other three profiling devices can be used to establish permanent networks for groundwater quality monitoring a suction type multilevel sampler consists of twenty or more narrow polyethylene or polypropylene tubes contained in a pvc casing that is capped at the bottom each tube extends to a different depth and is attached to a small screened sampling point that extends through the casing to draw water from the aquifer when suction is applied a positive displacement multilevel sampler is similar except that each sampling point is connected to a positive displacement pumping device located inside the pvc casing adjacent to the screen use of the suction type multilevel sampler is limited to zones where the water table is less than the suction lift depth of 8 or 9 m the positive displacement sampler can be used even if the water table is at a much greater depth a bundle piezometer consists of 1 2 cm o d flexible polyethylene tubes each with a short screened section at the bottom fastened as a bundle around a semi rigid center piezometer constructed of thick walled 2 cm o d pvc pipe in shallow water table areas water is withdrawn from each of the tubes and from the pvc piezometer by suction in areas with a deep water table samples are obtained by bailing with a narrow tube with a check valve on the bottom or by displacement using a double or triple tube gas drive sampler the positive displacement multilevel sampler or use of the gas drive samplers in the bundle piezometers provide the best opportunities for collecting samples that can be filtered and have preservatives added without the water being influenced excessively by degassing or by oxygen invasion networks of these three types of devices for multilevel groundwater monitoring were installed in the borden aquifer by means of hollow stem augers the devices are particularly well suited for use in aquifers composed of cohesionless sand or gravel that have little or no clay and groundwater flow that is primarily horizontal when 8 cm diameter hollow stem augers are used as many as eight polyethylene tubes are included conveniently in each bundle piezometer if augers with a larger hollow stem are used more tubes can be assembled in each bundle

field and modeling evidence for a stagnant flow zone in the upper meter of sandy phreatic aquifers abstract a stagnant flow zone where effective hydraulic conductivities are reduced by entrapped bubbles may be ubiquitous in the upper meter of the saturated zone in phreatic sand aquifers it is proposed that the stagnant zone acts as a thin semi aquitard within which groundwater flow paths tend toward the vertical once groundwater reaches the underlying active flow zone the flow paths are mainly horizontal in accordance with the aquifer hydraulic gradients the presence of stagnant zones in shallow groundwater is inferred from field and modeling data for three sand aquifer sites in southern ontario canada field data from an agricultural nitrate monitoring study and the vertical transport of a ground applied bromide tracer show clear evidence of a stagnant zone influence on solute distributions more direct evidence is provided by the analysis of data from multi point tracer tests akin to borehole tracer tests the inclusion of a stagnant zone in a numerical simulation of a septic effluent plume developed in an unconfined aquifer markedly improves the agreement between the simulated and field results potential mechanisms for the origin of bubbles in the stagnant zone are discussed since many contaminants traverse the upper meter of the saturated zone an increased understanding of the stagnant zone is important for monitoring and prediction of groundwater contamination

baked contact test demonstrates primary nature of dominant n1 magnetisation of nipissing intrusions in southern province canadian shield abstract nipissing diabase sills cone sheets and dykes define a major episode of igneous intrusion in the southern province of the canadian shield at about 2200 ma the dominant n1 remanence of these intrusions has been established in several palaeomagnetic studies and hence is a key tie point for the north american apparent polar wander path yet the age of this magnetisation remains very controversial positive baked contact tests reported for the n1 remanence have often been dismissed as inconclusive and the n1 palaeopole attributed to overprinting during the hudsonian orogeny 1900 1800 ma due to its position on a widely accepted polar wander path for north america previous baked contact studies utilise sediments of the huronian supergroup as host rock the remanence of these sediments is often difficult to interpret in this study a positive baked contact test is described for an n1 nipissing sill or cone sheet using stably magnetized mafic dykes of the matachewan swarm as host thus the n1 remanence is primary and no longer supports the time calibration of polar wander paths which assume that it is a 1900 1800 ma overprint

use of dissolved and vapor phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the subsurface 1 at many sites contaminated with petroleum hydrocarbons methanogenesis is a significant degradation pathway techniques to estimate ch4 production consumption and transport processes are needed to understand the geochemical system provide a complete carbon mass balance and quantify the hydrocarbon degradation rate dissolved and vapor phase gas data collected at a petroleum hydrocarbon contaminated site near bemidji minnesota demonstrate that naturally occurring nonreactive or relatively inert gases such as ar and n2 can be effectively used to better understand and quantify physical and chemical processes related to methanogenic activity in the subsurface in the vadose zone regions of ar and n2 depletion and enrichment are indicative of methanogenic and methanotrophic zones and concentration gradients between the regions suggest that reaction induced advection can be an important gas transport process in the saturated zone dissolved ar and n2 concentrations are used to quantify degassing driven by methanogenesis and also suggest that attenuation of methane along the flow path into the downgradient aquifer is largely controlled by physical processes slight but discernable preferential depletion of n2 over ar in both the saturated and unsaturated zones near the free phase oil suggests reactivity of n2 and is consistent with other evidence indicating that nitrogen fixation by microbial activity is taking place at this site

a dynamical model of high latitude convection derived from superdarn plasma drift measurements 1 a discrete set of climatological patterns of high latitude ionospheric convection are derived using line of sight plasma drift data from the super dual auroral radar network superdarn the patterns are derived independently for the northern hemisphere and southern hemisphere and for varying solar wind interplanetary magnetic field imf and dipole tilt angle conditions by interpolating between discrete patterns a dynamical model of convection is obtained which can uniquely specify the high latitude electrostatic potential distribution for a wide range of solar wind imf and dipole tilt parameter values accounting for solar wind velocity dependencies in convection leads to better resolving the large scale convection pattern as compared to previous statistical models based on superdarn data it is shown that the mesoscale features of the climatological model compare favorably to the features seen in instantaneous patterns of convection observed with superdarn comparison of the model to other statistical or empirical models derived from ground and space based measurements shows good agreement with most models

constraints on the nature of the kapuskasing structural zone from the study of proterozoic dyke swarms petrochemical paleomagnetic and structural studies on early proterozoic dyke swarms show that the rocks of the kapuskasing structural zone ksz central superior province were upthrust about 10 15 km along the ivanhoe lake fault after intrusion of 2 04 ga kapuskasing dykes this uplift was part of a more widespread deformation in flanking terranes that involved sinistral motion along north north northwest trending faults dextral displacement along east northeast northeast trending faults and a distortion of the 2 45 ga matachewan swarm to the west and northwest of the ivanhoe lake fault the most spectacular demonstration that the ksz is largely a product of proterozoic deformation is that matachewan dykes change their magnetic polarity on crossing the zone a consequence of remanence acquisition at deep crustal levels being delayed until after a reversal of the earth s magnetic field and prior to uplift of the dykes matachewan and kapuskasing dykes within the amphibolite to granulite grade rocks o

a positive fold test from nipissing diabase positive fold tests are reported on two remanence components resolved from the same nipissing diabase sills these tests conclusively indicate that the region south of the sudbury basin in the southern structural province has been subjected to two distinct deformational episodes subsequent to the intrusion of the nipissing diabase one event precedes 1850 2150 ma and one event postdates 1250 1850 ma intrusion of the sudbury irruptive some evidence also exists for a third event that may be related to the development of the sudbury structure around 1850 ma evidence that the nipissing was intruded into already folded huronian sediments confirms previous suggestions of four separate orogenic pulses in the period 2300 1250 ma

north south asymmetry of the high latitude thermospheric density imf by effect previous studies have established that the y component of the interplanetary magnetic field imf by plays a role in the north south asymmetry of the high latitude plasma convection and wind the effect of the positive negative imf by in the northern hemisphere resembles the effect that the negative positive imf by would have in the southern hemisphere in this study we demonstrate that the imf by effect can also contribute to the hemispheric asymmetry of the thermospheric density we use high accuracy air drag measurements from the challenging minisatellite payload champ satellite and supermag ae index during the period 2001 2006 to examine the response of the high latitude thermospheric density to geomagnetic activity our statistical analysis reveals that the density response at 400 km is greater in the southern hemisphere under positive imf by conditions and greater in the northern hemisphere under negative imf by conditions the results suggest that the imf by effect needs to be taken into account in upper atmospheric modeling for an accurate description of high latitude densities during periods of enhanced geomagnetic activity

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

effect of imf by on thermospheric composition at high and middle latitudes 1 numerical experiments 1 magnetic storms and their effects on the thermosphere and ionosphere have been studied for many years yet there are many aspects of the thermospheric and ionospheric responses that are not understood the purpose of this paper is to show how the high latitude composition depends on the sign of the imf by component using controlled simulations with a global first principles model because the high latitude convection and neutral wind systems are strongly controlled by the imf by component it seems likely that the compositional response that is driven by high latitude forcing should also be sensitive to the by component to date no first principles modeling has been performed to test the idea of imf by effects on composition numerical experiments using model simulations provide insight into this important scientific question since the thermospheric compositional response to the convection patterns for different imf bz and by can be studied in isolation in a model in this paper we use a first principles model to determine the effect of the imf by component on the compositional response of the high latitude thermosphere we show for the first time that a clockwise rotation of the potential pattern resulting from a change from by negative to by positive drives a corresponding rotation in the wind neutral density and composition distributions by control of thermospheric composition has been invoked in the literature to explain an apparent variability in the effectiveness of auroral activity in causing thermospheric storm effects at middle latitudes as observed in global images of the far ultraviolet fuv oi 130 4 nm emission from the de 1 auroral imager however the effect in the simulations presented here is opposite from that suggested by earlier work based on de data indicating another explanation must be sought for the de results these simulations are highly relevant for interpreting data being provided by more modern uv imaging instruments on the dmsp timed and image satellites

consolidation of continental crust in late archaean early proterozoic times a palaeomagnetic test abstract the proposition that continental crust consolidated during late archaean early proterozoic times as spatially distinct groups of cratons is tested using palaeomagnetic results assigned to the interval 2900 2200 ma geological data indicate the existence of two nuclei following widespread cratonisation at 2700 ma comprising ur stabilisation at 3000 ma and shallow water cover at 3000 2800 ma including central southern africa western australia and india and arctica which included laurentia fennoscandia and siberia stabilisation by 2500 ma with supracrustal cover beginning at 2400 ma a third nucleus atlantica comprising much of western africa and eastern south america consolidated later basement stabilisation at 2200 2000 ma and 2000 ma fluvial deltaic cover using this geometrical premise palaeomagnetic poles assigned to the interval 2900 2200 ma from the two older nuclei are observed to plot along two limbs of an apw swathe over 80 of the poles plot on a single segment running through the west of africa and terminating in a tight group over australia and india with ur resided in high latitudes and arctica in low latitudes the 2900 2200 ma mean poles from africa australia fennoscandia and laurentia also accord closely with one another and show that only small relative movements occurred between the cratons during these times this polar grouping does not result from datasets of similar temporal concentration and is due to low rates of continental movement 1 cm year that are probably the signature of small scale tectonic regimes the primeval continental crust consolidated as two linear belts with a configuration approximating to the geoid form and suggesting an aggregation by whole mantle convection the relative positions of arctica and ur at 2900 2200 ma were only marginally different from their positions within the putative later supercontinent of palaeopangaea 1100 550 ma and imply that the proterozoic eon was characterised by relatively small intracratonic motions close to limits of palaeomagnetic detection

migration of contaminants in groundwater at a landfill a case study 1 groundwater flow and plume delineation abstract a landfill derived contaminant plume with a maximum width of 600 m a length of 700 m and a maximum depth of 20 m in an unconfined sand aquifer was delineated by means of a monitoring network that includes standpipe piezometers multilevel point samplers and bundle piezometers the extent of detectable contamination caused by the landfill which began operation in 1940 and which became inactive in 1976 was determined from the distributions of chloride sulfate and electrical conductance in the sand aquifer all of which have levels in the leachate that are greatly above those in uncontaminated groundwater the maximum temperature of groundwater in the zone of contamination beneath the landfill is 12 c which is 4 5 c above background the thermal plume in the aquifer extends 150 m downgradient from the centre of the landfill a slight transient water table mound exists beneath the landfill in the late spring and summer in response to snowmelt and heavy rainfall beneath the landfill the zone of leachate contamination extends to the bottom of the aquifer apparently because of transient downward components of hydraulic gradient caused by the water table mound and possibly because of the higher density and lower viscosity of the contaminated water values of hydraulic conductivity which show variations due to local heterogeneity were obtained from slug tests of piezometers from pumping tests and from laboratory tests because of the inherent uncertainty in the aquifer parameter values the 38 yr frontal position of the plume calculated using the darcy equation with the assumption of plug flow can differ from the observed frontal position by many hundreds of metres although the use of mean parameter values produces a close agreement the width of the plume is large relative to the width of the landfill and can be accounted for primarily by variable periods of lateral east and westward flow caused by changes in water table configuration due to the variable nature of recharge northward from the landfill the vertical thickness of the plume decreases and the top of the plume is farther below the water table the thickness of the zone of uncontaminated groundwater above the plume increases northward as the area of recharge of uncontaminated water downflow from the landfill increases because dispersion in the vertical direction is weak there is very little mixing between the overlying zone of recharge water and the contaminant plume concentration profiles are irregular beneath and near the landfill and become smooth downgradient where the maximum concentrations are much less than those beneath landfill these features are attributed to a strong influence of longitudinal dispersion the plume passes beneath a small shallow stream near the landfill without significant influence on the stream

dissolved gas concentrations or concentration estimates a comment on origin distribution and hydrogeochemical controls on methane occurrences in shallow aquifers southwestern ontario canada by jennifer c mcintosh stephen e grasby stewart m hamilton and stephen g osborn

on the incorporation of drains into three dimensional variably saturated groundwater flow models subsurface drains are important features in many problems involving shallow groundwater flow and have generally been represented in two dimensional numerical models by specifying hydraulic head or fluid flux at one or more nodes in the computational grid here we describe a new approach for representing drains in three dimensional variably saturated flow models the method is based on a one dimensional flow equation for the drain which is analogous to a one dimensional open channel flow equation the numerical contributions to the system of global equations from the one dimensional discretized equation are added to the three dimensional porous medium contributions the inclusion of drain flow by this technique is readily adaptable to any three dimensional numerical simulator the accuracy of the method is demonstrated by comparing results obtained with the new method to steady state and transient results presented by fipps et al 1986 the numerical formulation naturally accommodates flow in heterogeneous media and demonstrates excellent mass balance illustrative examples are presented which highlight the usefulness of the algorithm for studying the influence of drains in problems involving subsurface effluent disposal in heterogeneous aquifers and agricultural land drainage the method will have application to many studies involving water and contaminant movement in drained soils

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 1 experimental design and observed tracer movement a large scale natural gradient tracer experiment was conducted on cape cod massachusetts to examine the transport and dispersion of solutes in a sand and gravel aquifer the nonreactive tracer bromide and the reactive tracers lithium and molybdate were injected as a pulse in july 1985 and monitored in three dimensions as they moved as far as 280 m down gradient through an array of multilevel samplers the bromide cloud moved horizontally at a rate of 0 42 m per day it also moved downward about 4 m because of density induced sinking early in the test and accretion of areal recharge from precipitation after 200 m of transport the bromide cloud had spread more than 80 m in the direction of flow but was only 14 m wide and 4 6 m thick the lithium and molybdate clouds followed the same path as the bromide cloud but their rates of movement were retarded about 50 relative to bromide movement because of sorption onto the sediments