Gypsum sulfur isotopes

Kamineni D. C. (1983) Sulfur-isotope geochemistry of fracture filling gypsum in an Archean granite near Atikokan, Ontario, Canada. Chem. Geol. 39, 263-272. 

The mixing time of S04 in the ocean is short compared to its residence time. Thus, the isotopic composition of S04 in seawater is constant over geologically short time periods. One pathway for removal of this seawater sulfate is by precipitation of sulfate-bearing evaporite minerals. When marine evaporite minerals such as gypsum (CaS04 2H20) precipitate from seawater, the sulfur isotope fractionation between the aqueous and solid-phase sulfate is very small, about -b 1.7%o (Thode and Monster, 1965). The combination of these factors implies that contemporaneous marine evaporites have the same isotopic composition worldwide, and they are nearly identical isotopically to seawater SO of that age. When the sulfur isotopic composition of marine evaporite S04 is plotted as a function of... 

Sulfur is shown on Figure 3 as SO3, which includes organic and inorganic sulfur. Direct observations and isotopic composition of sulfur (5) indicate that kerogen-bound sulfur accounts for 60-80% of the total sulfur in the rock while the remainder is pyritic and gypsum sulfur. 

In all samples studied, of pyrite is the most depleted. The OM sulfur is on average 10%c heavier a very small amount of the sulfate minerals gypsum and anhydrite for the Nabi Musa location indicates evaporative conditions and sulfate closed system. Despite the same Senonian Ghareb Formation sedimentary rock for aU of the Dead Sea area samples studied, the values recorded for different sites show wide variability. This indicates that small differences in sub-basin conditions have a significant imprint on sulfur isotope distribution. 

Jaworska J. 2010 - An oxygen and sulfur isotopic study of gypsum from the Wapno Salt Dome cap-rock (Poland). Geological Quarterly, 54,1 25-32. 

The principal sources of sulfate in formation waters are dissolved marine sulfate, sulfate derived from the dissolution of evaporites, and sulfate formed by the oxidation of sulfides. Sulfate is destroyed by reduction to hydrogen sulfide. The value of 5 " S in gypsum is only — 1.6%o heavier than sulfate in solutions from which it precipitates. The isotopic composition of sulfur in gypsum in Phanerozoic deposits precipitated from seawater during evaporation thus tracks the secular changes in the isotopic composition of sulfur in seawater ( 10% to 30%o). 

Faure G, Felder RP (1981) Isotopic composition of strontium and sulfur in secondary gypsum crystals. Brown Hills, Transantarctic Mountains. J Geochem Explor 14 ... 

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