Origin and distribution of sulfate in a fractured till in southern Alberta, Canada
Glacial till in a 22-km/sup 2/ area of the Interior Plains Region of southern Alberta, Canada consists of an upper brown gypsiferous weathered zone (up to 20 m thick) and a lower discontinuous grey nonweathered zone (up to 25 m thick). Although the total sulfur content of the two till zones is the same (0.34%), the mean total sulfate content of the weathered till (4.0 mg g/sup -1/) exceeds that the nonweathered till (0.8 mg g/sup -1/). Similarities suggest that all SO/sub 4//sup 2 -/ in the nonweathered till and 20% of the sulfate in the weathered till was derived from sulfate-rich bedrock fragments incorporated in the till during deposition. Laboratory experiments and delta/sup 18/O and delta/sup 34/S analyses of total SO/sub 4//sup 2 -/ and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic S at some time after the till was deposited. Mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions. Groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier Altithermal period (11,000 to 3000 years B.P.). The following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed. The oxidation of reduced S produced SO/sub 4//sup 2 -/ and H/sup +/. The H/sup +/ reacted with carbonate minerals under elevated p/sub CO2/, with Ca/sup 2 +/ loss by exchange for Na/sup +/ and gypsum precipitation. Volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity.
- Research Organization:
- Alberta Agriculture, Edmonton
- OSTI ID:
- 5455556
- Journal Information:
- Water Resour. Res.; (United States), Journal Name: Water Resour. Res.; (United States) Vol. 22:1; ISSN WRERA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580100* -- Geology & Hydrology-- (-1989)
ALBERTA
CANADA
CARBON COMPOUNDS
CARBONATES
CHEMICAL COMPOSITION
CHEMISTRY
COMPUTERIZED SIMULATION
EVEN-EVEN NUCLEI
GEOCHEMISTRY
GROUND WATER
HYDROGEN COMPOUNDS
ISOTOPE APPLICATIONS
ISOTOPES
LIGHT NUCLEI
NATURAL OCCURRENCE
NORTH AMERICA
NUCLEI
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
SIMULATION
SOIL CHEMISTRY
SOILS
STABLE ISOTOPES
SULFATES
SULFUR 34
SULFUR COMPOUNDS
SULFUR ISOTOPES
TRACER TECHNIQUES
WATER
WEATHERING