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Regional geochemical characterization of groundwaters in a bedrock aquifer in the Ottawa--St. Lawrence Lowlands of eastern Ontario has identified an iodine (I) anomaly, with values regularly exceeding 150 [micro]g/L and a maximum observed concentration of 10 812 [micro]g/L. The spatial distribution, enrichment mechanisms, and sources of I and organic matter were investigated using geochemical and isotopic data. High-I groundwaters (>150 [micro]g/L) are prevalent in Na-Cl-type groundwaters at low bedrock elevations in areas overlain by thick layers of glacial sediments. I is thought to be linked to massive muds in the glacial sediments overlying the aquifer, deposited during the postglacial incursion of the Champlain Sea 12-10 ka BP. Principal component analysis of I and 18 other chemical parameters revealed correlations among I, salinity, and indicators of microbial oxidation of organic matter, suggesting that the intrusion of saline pore waters affected by decomposition of organic matter such as marine phytoplankton in the massive muds is the dominant process controlling I enrichment in groundwater. [.sup.129]I/[.sup.127]I ratios in the pre-modern waters vary between near-marine values of 460 x [10.sup.-14] and 5 x [10.sup.-14], demonstrating that older allochthonous I derived from the surrounding Paleozoic sedimentary terrain also contributed to the I pool in the Champlain Sea basin. [.sup.14]C ages and [delta][.sup.13]C signatures for dissolved organic carbon in groundwater and disseminated organic carbon within the glaciomarine muds highlight an allochthonous source of terrestrial organic carbon predating the Champlain Sea incursion, likely transported via glacial meltwaters in tandem with I to the Champlain Sea basin. La caracterisation geochimique regionale des eaux souterraines dans un aquifere rocheux dans les Basses Terres de l'Outaouais et du Saint-Laurent de l'est de l'Ontario a fait ressortir une anomalie d'iode (I), avec des valeurs excedant regulierement 150 [micro]g/L et une concentration maximum observee de 10 812 [micro]g/L. La repartition spatiale, les mecanismes d'enrichissement et les sources d'I et de matiere organique ont ete examines en utilisant des donnees geochimiques et isotopiques. Des eaux souterraines riches en I (>150 [micro]g/L) sont courantes parmi les eaux souterraines de type Na-Cl a de faibles elevations dans le socle rocheux dans des zones sur lesquelles reposent d'epaisses couches de sediments glaciaires. L'I serait relie a des argiles massives dans les sediments glaciaires reposant sur l'aquifere, deposees durant l'incursion postglaciaire de la mer de Champlain il y a 12-10 ka BP. L'analyse en composantes principales de l'I et de 18 autres parametres chimiques revele des correlations entre l'I, la salinite et des indicateurs d'oxydation microbienne de la matiere organique qui donnent a penser que l'intrusion d'eaux interstitielles salines influencees par la decomposition de matiere organique comme du phytoplancton marin dans les argiles massives est le principal processus modulant l'enrichissement en I de l'eau souterraine. Les rapports [.sup.129]I/[.sup.127]I dans les eaux premodernes vont de 460 x [10.sup.-14] a 5 x [10.sup.-14], des valeurs quasi marines, ce qui demontre que de l'I allochtone plus ancien derive du terrain sedimentaire paleozoique environnant a aussi contribue au reservoir d'I dans le bassin de la mer de Champlain. Les ages [.sup.14]C et les signatures de [delta][.sup.13]C pour le carbone organique dissous dans l'eau souterraine et le carbone organique dissemine dans les argiles glaciomarines font ressortir la presence de carbone organique terrestre provenant d'une source allochtone plus ancienne que l'incursion de la mer de Champlain, vraisemblablement transporte de pair avec l'I dans le bassin de la mer de Champlain par des eaux de fonte glaciaires. [Traduit par la Redaction], Introduction Geochemical analysis of shallow groundwaters ( The phenomenon of I enrichment in groundwater affects many regions of the world, including Japan (Kashiwagi et al. 2006; Togo et al. 2016), [...]

Porewater extractions and acid leachates of rock core from a 250 m thick sequence of low-permeability Ordovician-age shales and limestones, on the eastern flank of the Michigan Basin, were analysed for strontium isotope ratios in an attempt to infer porewater ages from observed [.sup.87]Sr/[.sup.86]Sr enrichments. The porewaters originated as Ordovician seawater, which subsequently mixed with evaporated Silurian seawater infiltrating from above, and, to some extent, with a deep brine--with an enriched [.sup.87]Sr/[.sup.86]Sr signature--from the underlying crystalline shield or deep basin. The porewater [.sup.87]Sr/[.sup.86]Sr ratios are more radiogenic than contemporaneous seawater but show no obvious correlation to those leached from the solid rock phases. Accepting that the initial [.sup.87]Sr/[.sup.86]Sr signatures in porewaters were dominated by Late Silurian brine, potentially with an additional deep brine component, the excess of radiogenic [.sup.87]Sr appears to represent ingrowth from [.sup.87]Rb decay over a time span of some 420 million years, approaching the depositional age of the rocks. Similarly, Rb/Sr errochron ages of acid leachates of solid phases, and the calculated initial [.sup.87]Sr/[.sup.86]Sr isotopic ratios, are consistent with a proposition that the calcites inherited their Sr from Ordovician seawater and were dolomitized shortly afterwards by infiltrating Mg-enriched evaporative brine, indicating long-term conservative behaviour for the enclosing carbonate rocks. The errochron for leachates from (alumino)silicates yields a high initial [.sup.87]Sr/[.sup.86]Sr, but with an errochron age of about 340 [+ or -] 48 Ma, likely owing to variable admixtures of diagenetic illite in the shales. Overall, the data provide evidence for a stable hydrologic regime since Paleozoic time. Des extractions d'eau interstitielle et de lixiviats acides de carottes de roches d'une sequence de 250 m d'epaisseur de shales et calcaires ordoviciens de faible permeabilite sur le flanc est du bassin du Michigan ont ete analysees pour en determiner les rapports d'isotopes du strontium, dans le but d'inferer les ages des eaux interstitielles sur la base de l'enrichissement observe en [.sup.87]Sr/[.sup.86]Sr. Les eaux interstitielles etaient a l'origine de l'eau de mer ordovicienne qui s'est ensuite melangee avec de l'eau de mer silurienne evaporee s'infiltrant par le haut et, dans une certaine mesure, avec une saumure profonde--caracterisee une signature en [.sup.87]Sr/[.sup.86]Sr enrichie--provenant du bouclier cristallin ou bassin profond sous-jacent. Les rapports [.sup.87]Sr/[.sup.86]Sr des eaux interstitielles sont plus radiogeniques que ceux de l'eau de mer contemporaine, mais ne presentent aucune correlation evidente avec les eaux lixiviees des phases solides des roches. En presumant que les signatures initiales de [.sup.87]Sr/[.sup.86]Sr dans les eaux interstitielles etaient dominees par des saumures d'age silurien tardif et, eventuellement, par une autre composante de saumure profonde, l'excedent de[.sup.87]Sr radiogenique semble representerle resultatde ladecomposition du[.sup.87]Rb sur une periode dequelque 420 millions d'annees, s'approchant de l'age du depot des roches. De meme, les ages erreurchrones de lixiviats acides issus de phases solides et les rapports [.sup.87]Sr/[.sup.86]Sr initiaux calcules concordent avec la proposition voulant que les calcites aient herite leur Sr d'eau de mer ordovicienne et ont ete dolomitisees peu apres par une saumure issue de l'evaporation enrichie en Mg, ce qui temoigne d'un comportement conservateur a long terme des roches carbonatees encaissantes. L'errochrone pour les lixiviats d'(alumino)silicates donne un [.sup.87]Sr/[.sup.86]Sr initial eleve, mais avec un age errochrone d'environ 340 [+ or -] 48 Ma, decoulant probablement de degres variables de melange d'illite diagenetique dans les shales. Globalement, les donnees offrent des preuves d'un regime hydrologique stable depuis le Paleozoique. [Traduit par la Redaction], Introduction A 400 m thick Upper Ordovician sedimentary sequence of shale (200 m) and underlying carbonate (200 m) situated on the eastern flank of the Michigan Basin comprise an aquiclude [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.05.017 Byline: Denis Lacelle (a), David Fisher (b), Ian D. Clark (c), Alain Berinstain (a) Keywords: Mars; polar geology; Geological processes Abstract: In this study, various approaches that can potentially distinguish between vapor- and liquid-derived ground ice in the martian regolith (petrography, geochemistry, stable OH isotopes, CO.sub.2 O.sub.2 N.sub.2 Ar gas composition) are examined using terrestrial ground ice examples. Although the stable OH isotope composition ratios can distinguish between vapor- and liquid-derived terrestrial ground ice, there might be to much mixing between the various water reservoirs on Mars to effectively use it, and, like on Earth, petrographic and geochemical approaches need to be complemented with additional supporting evidences. Of the different approaches currently being employed to determine the origin of terrestrial massive ground ice and icy sediments, it is the concentration of CO.sub.2 and the O.sub.2/Ar, N.sub.2/Ar and N.sub.2/O.sub.2 ratios of air entrapped in the ice that has proven to be the less ambiguous and most discriminatory. This is because the molar ratios of atmospheric gases change during their dissolution in water due to differences in their relative solubilities, thus providing distinctive ratios for the dissolved gases. The gas composition of air entrapped in the ice not only distinguishes between vapor- and liquid-derived ground ice, but any deviation from the theoretical dissolved values can provide insights into potential physical and biological processes operating in the subsurface, a key component for astrobiology. Author Affiliation: (a) Planetary Exploration and Space Astronomy, Canadian Space Agency, 6767 route de l'aeroport, St-Hubert, QC, J3Y 8Y9, Canada (b) Glaciology Section, Geological Survey of Canada, NRCan, 601 Booth Street, Ottawa, ON, K1A 0E8, Canada (c) Ottawa-Carleton Geoscience Center, Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, ON, K1N 6N5, Canada Article History: Received 19 March 2008; Revised 22 May 2008

This study examines the physical and geochemical properties of near-surface sediments, as well as the geochemical and stable O-H-C isotope composition of (ground)surface waters in and around the Haughton impact structure region (Devon Island, Nunavut) to determine the types of weathering (mechanical, (bio)chemical) and their relative contribution in this polar desert environment. The surface sediments collected from the Allen Bay and Thumb Mountain formations surrounding the impact crater are dominated by sand-sized particles; whereas the impact melt breccias inside the crater have a greater abundance of silt-sized particles. The subsurface sediments in the Allen Bay formation show a near equal amount of sand- and silt-sized particles. However, the micromorphologies of the sand-sized particles collected at the surface revealed that these grains, irrespective of the local geology, were heavily fractured. By contrast, fractures and rounded pits are observed on the surface of the sand grains located within the active layer; whereas those located just above the permafrost table have only rounded cavities on their surface. The (ground)waters also show variations in their solute concentration with depth; the highest concentrations being found in the groundwaters near the top of permafrost. Taken together, these observations suggest that there is a progressive evolution from a mechanically dominated weathering regime near the surface, to increasing chemical weathering with depth. The transition from mechanical weathering near the surface to increasing chemical weathering with depth can be attributed to the decreasing frequency and intensity of mechanical weathering processes (i.e., frost action, wetting- drying, thermal dilation) with depth, and to the presence of permafrost, which allows a greater availability of water for chemical aqueous reactions at the base of the active layer. Cette etude examine les proprietes physiques et geochimiques de sediments pres de la surface ainsi que la composition geochimique et la composition des isotopes stables O-H-C des eaux souterraines et de surface dans la region de la structure d'impact Haughton et autour de celle-ci (ile Devon, Nunavut) afin de determiner le type de meteorisation (mecanique, (bio)chimique) et leur contribution relative dans cet environnement de desert polaire. Les sediments de surface recueillis des formations d'Allen Bay et de Thumb Mountain entourant le cratere d'impact comprennent surtout des particules de la taille du sable, alors que les breches de fusion d'impact a l'interieur du cratere presentent plus de particules de la taille du silt. Les sediments sous la surface dans la Formation d'Allen Bay montrent des quantites presque egales de particules de la taille du sable et du silt. Toutefois, la micromorphologie des particules de la taille du sable recueillies a la surface revele que ces grains etaient grandement fractures, peu importe la geologie locale. Cependant, des fractures et de petites depressions arrondies sont observees a la surface des grains de sable situes dans la couche active, alors que les particules situees tout juste au-dessus de la nappe du pergelisol ne presentent que des cavites arrondies a leur surface. Les eaux souterraines presentent aussi des variations de concentration de solute avec la profondeur; les plus hautes concentrations se retrouvent dans les eaux de surface pres du sommet du pergelisol. Prises ensemble, ces observations suggerent qu'il existe une evolution progressive d'un regime d'alteration principalement mecanique pres de la surface a une alteration de plus en plus chimique avec la profondeur. La transition d'une alteration mecanique a proximite de la surface a une alteration chimique plus poussee avec la profondeur peut etre attribuee a la frequence et l'intensite decroissantes des processus d'alteration mecanique (c.-a-d. l'action du gel, les cycles de mouillage et sechage, la dilatation thermique) avec la profondeur et a la presence du pergelisol qui permet une plus grande disponibilite d'eau pour des reactions chimiques aqueuses a la base de la couche active. [Traduit par la Redaction], Introduction In periglacial environments, weathering processes (i.e., mechanical, chemical, and biological) occur mainly in the active layer, which is the top layer of soil that undergoes annual freezing and thawing. [...]

Abstract: This study documents the discovery of calcite crusts on the upper surface of clasts within morainic complexes in Akshayuk Pass, southern Cumberland Peninsula (Baffin Island), a region underlain by [...]

Canadian Shield brines are characterized by high concentrations of both stable iodine and [sup.129]I, the former reflecting its concentrated but diagenetically modified seawater origin, and the latter its long subsurface residence time within its host shield rocks. Stable iodine concentrations in the Yellowknife brine are as high as 18 mg/L, requiring the contribution of iodine from an external marine reservoir. This reservoir likely comprised organic-rich marine sediments in the basin where the brine was produced. Diagenesis of these sediments released iodine to the brine during its infiltration into the subsurface. [sup.129]I concentrations in the Yellow-knife brine are as high as 3.4 x [10.sup.8] atom/L and are due to the fission of [sup.238]U in the rock matrix and subsequent diffusion of the radiogenic [sup.129]I into the fracture fluids. This concentration is close to the predicted secular equilibrium concentration for a fluid in basaltic rock with a uranium concentration of 1 mg/kg after the residence time of ~80 m.y. required for secular equilibrium has been attained. This time period is interpreted as the minimum residence time of the Yellowknife brine in the shield, but it may be much greater, possibly dating back to Middle Devonian time when most of the present-day shield was covered by seawater. Similarly high stable iodine and [sup.129]I concentrations measured in the Sudbury brine support a generic, ancient marine hypothesis for the origin of shield brines. Stable iodine and [sup.129]I concentrations in the shallower mine waters are the result of mixing between the brine and low-iodine modern meteoric recharge that is enriched in [sup.129]I due to global fallout from nuclear fuel waste reprocessing activities. Keywords: shield brines, marine, iodine, iodine-129, residence time.

Introduction Ground water is the dominant water resource in most agricultural watersheds, yet its quality is threatened by the very population and industry that it supports. Assessing the risk of [...]

Ian D. Clark [a] Malcolm Douglas [b] Kenneth Raven © Dennis Bottomley [d] Abstract Ground water inflows to drifts ranging from 700 to 1615 m below ground surface at the [...]