Degree Granting Department
Bogdan Onac, Ph.D.
Jonathan Wynn, Ph.D.
Henry L. Vacher, Ph.D.
Stable isotope, Karst, Geochemistry, Mineralogy, Sulfuric acid speleogenesis
Baile Herculane, located in southwestern Romania, is a unique city that exploits its thermal waters. The geology consists of a granitic basement covered by 200 meters of limestone, marl, and flysch deposits. Extreme faulting carries heat ascending from the mantle, which intercepts percolating meteoric waters. Local springs have high concentrations of dissolved sulfide gas (H2S) and dissolved sulfate (SO4²-).These dissolved species indicate the progression of sulfate reduction in the aquifer.
Water samples were collected in polyethylene syringes to prevent oxidation of sulfide. Then, sulfide and sulfate were quantitatively reacted for stable isotope analysis. Total sulfur isotopic composition was calculated to determine the source of the dissolved sulfur. The source of the sulfur is a sulfate of marine origin (𝛅34S≅20%0), which I found to come from impurities in the limestone since the Cerna Valley does not possess marine evaporites.
The limestones of the Cerna Valley are host to a number of caves, which possess relatively large deposits of sulfates and exotic morphologic features that suggest speleogenesis by sulfuric acid. 𝛅34S of the sulfates relates to sulfide isotopic values from the springs, showing that the dissolved sulfide (upon oxidation) forms sulfuric acid s that reacts with limestone to produce sulfate minerals. A wide range of cave sulfate 𝛅34S values exist indicating that isotopic values of these deposits depend on several factors such as sulfur source, extent of sulfate reduction, and completeness of sulfide oxidation. This also implies that a single, narrow range of sulfur isotopic values does not represent sulfuric acid speleogenesis.
Scholar Commons Citation
Sumrall, Jonathan, "Using 34-S as a Tracer of Dissolved Sulfur Species from Springs to Cave Sulfate Deposits in the Cerna Valley, Romania" (2009). USF Tampa Graduate Theses and Dissertations.