Delta 34S and delta 18O variations in terrestrial sulfates
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AbstractIn this thesis, oxygen and sulfur isotope analyses of over 300 samples from diverse environments are employ ed to comprehend multifarious processes in sulfate geochemistry. Experimental techniques for the measurement of o18o and o34s values of sulfates were considerably modified to expedite analyses and obtain better precision. o1 8 O values were measured on co2 produced by graphite reduction of Baso4 • For this conversion, a stainless steel reactor was built into which four samples could be loaded simultaneously into platinum canoes. By resistance heating, a given canoe achieved a temperature in excess of l000°c within a few seconds, thus promoting faster and more reproducible conversions. o34s analyses were done on so2 produced by the direct 0 reduction of Baso4 with NaP03 at 900 C, thus reducing the number of wet chemical analytical steps normally associated with sulfur isotope analyses. Gypsum and anhydrite obtained from evaporite sections, drill-cores, outcrops, and cements were studied. Isotopic criteria were developed for discriminating secondary alteration products from primary deposits. In conjunction with analyses of complete evaporite sections, these criteria can be used to reduce uncertainties in the oceanic so2- 4 isotopic composition-age curves. Isotopic data from evaporite cores were used to locate the position of a thrust-fault in the Norman Range, N.W.T. where Lower Devonian strata are unconformably overlain by Upper Cambrian strata. Criteria were established for using isotopic data from marine barites in constructing the oceanic sof- isotopic composition-age curve. Freshwater wells, springs, and associated deposits were also studied. o-values were used to distinguish oxidation of metal sulfides from dissolution of evaporites as provenances of so2- 4 in springs. Such studies can identify and locate non-outcropping ore-deposits. o-values of airborne and fallout species associated with some springs delineated complex microbiological and chemical water-airrock interactions. As an example, cave formation at Banff was found to involve microbial-chemical reactions rather than simple physical erosion. In addition to more common travertine and tufa deposits, rare deposits of jarosite and barite associated with springs were also examined, including a radioactive barite sinter deposit in the District of MacKenzie, N. W.T. In the majority of these studies, o 18o values provided more information than obtained from o34s values alone. In many cases, reduction of so2- 4 to HS and reoxidation back to so24 - could not be ascertained from the o34s data. However, the o18o data revealed this phenomenon since isotopically different oxygen from water and air was incorporated during the reoxidation.
Bibliography: p. 214-229.
CitationShakur, M. A. (1982). Delta 34S and delta 18O variations in terrestrial sulfates (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/22320
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