Related Papers
Geochimica et Cosmochimica Acta
Dating ultra-deep mine waters with noble gases and 36Cl, Witwatersrand Basin, South Africa
2003 •
Duane Moser
Establishing constraints on groundwater ages with 36Cl, 14C, 3H, and noble gases: A case study in the eastern Paris basin, France
D. Bourlès
Groundwaters from the Tithonian/Kimmeridgian, Oxfordian and Upper Dogger aquifers, within the eastern part of the Paris basin (France), were characterised using 3H, 14C and 36Cl, and noble gases tracers, to evaluate their residence times and determine their recharge period. This information is an important pre- requisite to evaluating the confinement properties of the Callovo-Oxfordian clay formation sandwiched between the Oxfordian aquifer and the Dogger aquifer, currently being investigated by the French nuclear waste management agency (Andra) for radioactive waste disposal. Data presented in this paper are used to test 4 hypotheses. (1) The Oxfordian limestone is isolated from the overlying Tithonian/Kimmeridgian surface aquifer. This first hypothesis is supported by the presence of measurable 3H activities in groundwaters from the surface aquifer (6–11 TU), and by its absence in groundwaters derived from deeper aquifers (<3 TU), as well as by geochemical data from earlier studies. (2) The Callovo-Oxfordian clay sequence in the vicinity of the URL serves as an effective barrier to advective flow and transport between the underlying Upper Dogger aquifer and the overlying Oxfordian limestone aquifer. This second hypothesis is supported by relatively low concentrations of Cl (3.5–78 mg.L-1), Na (15–145 mg.L-1), Br (0.08–0.4 mg.L-1) and 4Herad (0.2–2.3 ccSTP.g-1) and slightly higher 36Cl/Cl ratios (2.7–59x10-15 at.at-1) in groundwaters from the Oxfordian aquifer, compared to those from the Upper Dogger aquifer (345–4027 mgCl.L-1 ; 402–2390 mgNa.L-1 ; 1.8–22.2 mgBr.L-1 ; 1.6–37.2 ccSTP He g-1 ; 1–5x10-15 at36Cl.at -1Cl). (3) Groundwaters from the Oxfordian aquifer, in the vicinity of URL are pre-Holocene, with residence times exceeding 10 ka. Geochemical and isotopic lines of evidence for this hypothesis include:(a) delta13C values measured on Oxfordian aquifer waters that are close to delta13C of the aquifer matrix, reflecting strong isotopic exchange over several thousand years; (b) noble-gas temperatures that indicate recharge temperatures between 3 and 8.6°C, lower by 2–7°C than the modern average temperature in this area ; (c) radiogenic 4He concentrations between 0.16x10-5 and 2.3x10-5 ccSTP.g-1 of water, about 2–3 orders of magnitude greater than the 4He concentration of air-equilibrated water. (4) Groundwater residence time for the Upper Dogger aquifer in the vicinity of the URL probably exceed several hundred thousand years. Such long residence times are indicated by the accumulation of radiogenic He-up to 37x10-5 ccSTP.g-1 assuming a closed system.Primary contributors to uncertainties in interpretation of the data presented in this paper are the lack of: – well-defined 36Cl/Cl input ratio; – knowledge about the 4Herad sources for Oxfordian and Dogger aquifers; – knowledge about transport processes occurring through the Dogger aquifer, and the extensive dilution of initial 14C activities by dissolution/exchange with aquifer matrix. Overall, however, although the data presented in this paper remain semi-quantitative due to inevitable intrinsic limitations of the methods, none contradict the hypotheses of long residence times and aquifer isolation in the vicinity of the URL.
Groundwater dynamics, paleoclimate and noble gases
1999 •
Urs Beyerle
Geochimica et Cosmochimica Acta
Comment on “Improving noble gas based paleoclimate reconstruction and groundwater dating using 20Ne/22Ne ratios,” by Geochim. Cosmochim. Acta, 67, 587–600
2004 •
Abdou GUERO
Nature
Palaeotemperature reconstruction from noble gases in ground water taking into account equilibration with entrapped air
Applied Geochemistry
Major and trace element geochemistry in Zeekoevlei, South Africa: A lacustrine record of present and past processes
2008 •
Supriyo Das
This study reports a multi-parameter geochemical investigation in water and sediments of a shallow hyper-eutrophic urban freshwater coastal lake, Zeekoevlei, in South Africa. Zeekoevlei receives a greater fraction of dissolved major and trace elements from natural sources (e.g., chemical weathering and sea salt). Fertilizers, agricultural wastes, raw sewage effluents and road runoff in contrast, constitute the predominant anthropogenic sources, which supply As, Cd, Cu, Pb and Zn in this lake. The overall low dissolved metal load results from negligible industrial pollution, high pH and elevated metal uptake by phytoplankton. However, the surface sediments are highly polluted with Pb, Cd and Zn. Wind-induced sediment resuspension results in increased particulate and dissolved element concentrations in bottom waters. Low C/N ratio (10) indicates primarily an algal source for the sedimentary organic matter. Variation in sedimentary organic C content with depth indicates a change in primary productivity in response to historical events (e.g., seepage from wastewater treatment plant, dredging and urbanization). Primary productivity controls the enrichment of most of the metals in sediments, and elevated productivity with higher accumulation of planktonic debris (and siltation) results in increased element concentration in surface and deeper sediments. Aluminium, Fe and/or Mn oxy-hydroxides, clay minerals and calcareous sediments also play an important role in adsorbing metals in Zeekoevlei sediments.
Earth-Science Reviews
Archaean atmospheric evolution: evidence from the Witwatersrand gold fields, South Africa
2005 •
Hartwig Frimmel
Geomicrobiology Journal
The Origin and Age of Biogeochemical Trends in Deep Fracture Water of the Witwatersrand Basin, South Africa
2006 •
Gordon Southam
Special Paper of the Geological Society of America
The nature of hydrocarbons and related fluids in the Witwatersrand Basin, South Africa: Their role in metal redistribution
Laurence Robb
Gold and uranium mineralization within the Archean Witwatersrand Basin exhibits a close association with carbonaceous matter. In order to understand the gold and uranium mineralization associations, it is necessary to understand something about the carbonaceous matter itself as well as the fluids involved in remobilizing both hydrocarbons and mineralization within the basin. Diagenetic maturation of primitive bacterial material released hydrocarbons that were able to migrate through the sediments of the economically important Wit-watersrand Basin. Migrating hydrocarbons underwent polymerization and conden-sation due to the effect of ionizing radiation in the proximity of detrital uraninite during catagenesis. Isotopically heavy hydrocarbons precipitated out as bitumen seams where uraninite concentrations were high or as "fly-speck" bitumen around isolated uraninite grains, giving rise to sediment-hosted bitumen types. Lighter hydrocarbons, liberated during catagenic radiol...
