Perry, Eugene C., 1933-
M.S. (Master of Science)
Department of Geology
Evaporites; Sulphur--Isotopes; Geology; Stratigraphic--Precambrian
The sulfur isotope composition of marine sulfate evaporites defines a secular trend extending from the late Proterozoic through the Phanerozoic. This trend reflects the compositional variability of seawater sulfate with time. Data derived from preserved Precambrian anhydrite or gypsum are scarce, although replaced evaporites are recognized throughout virtually the entire geologic record. Many such replaced evaporites contain carbonate and silica pseudomorphs that preserve the morphology of the original sulfate minerals. A possible new recorder of seawater sulfate is tested here on an occurrence of anhydrite inclusions within Lower Proterozoic silicified evaporites of the Kona Dolomite (Marquette region, Michigan), along with other samples exhibiting relict textures of evaporite deposition. I report a mean δ³⁴S value of +13.3°/∘∘ for traces of anhydrite preserved within silica pseudomorphs of the Kona Formation; other samples yielded insufficient amounts of sulfate for analysis and, therefore, results were inconclusive. Although effects of diagenetic replacement and low-grade metamorphism are undetermined, strontium isotope data for the Kona sediments indicate that the derived δ³⁴S value may represent a minimum δ³⁴S for seawater sulfate at about 2.0 Ga (10⁹ yrs ago).
Hemzacek, Jean Marie, "Replaced evaporites and the sulfur isotope age curve of the Precambrian" (1987). Graduate Research Theses & Dissertations. 4732.
v, 77 pages
Northern Illinois University
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