Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the Cerna Valley, Romania
- Permanent Link:
- Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the Cerna Valley, Romania
- Series Title:
- Chemical Geology
- Wynn, Jonathan G.
Sumrall, Jonathan B.
Onac, Bogdan P.
- Publication Date:
- Subjects / Keywords:
- Sulfur Isotope ( local )
Sulfate Reduction ( local )
Thermo-Mineral Springs ( local )
Sulfide ( local )
Sulfate ( local )
- serial ( sobekcm )
- Documenting the source and processes controlling dissolved sulfur (S) mineralization in thermo-mineral waters of the Cerna Valley, Romania is important to understanding speleogenesis in this karst region, in addition to understanding hydrogeological controls, therapeutic qualities and sustainability of the region's historic spas. Stable S and carbon (C) isotopic results reported here elucidate controls on redox processes, the source of dissolved S mineralization, and sulfur-bearing mineral precipitation in this unique karst hydrothermal system. At reservoir temperatures that occur in the Cerna Valley aquifers, it is likely that thermochemical sulfate reduction (TSR) is the dominant S reduction pathway. However the apparent isotope enrichment that we observed between coexisting dissolved sulfate and sulfide is higher than normally associated with TSRâ€”a fact that likely reflects rapid redox cycling at low grade hydrothermal temperatures. Î´13C values of dissolved inorganic carbon (DIC) are consistent with TSR using methane as an electron donor. Î´34S values of total dissolved S (sum of sulfide and sulfate) in all springs sampled and particularly in those for which closed-system conditions can be demonstrated, is greater than + 16â€°, consistently pointing to dissolved S that derives from marine-derived sulfate mineral sources. To this combined Sâ€“C isotope data set, we apply a model of Rayleigh distillation which describes exponentially increasing Î´34S values of a diminishing sulfate reservoir during TSR, and linearly decreasing Î´13C values of DIC indicating mixing of C from the electron donor involved in TSR. Comparison of our results to this model shows two distinct stages of TSR during transport of fresh water from karst aquifers towards the local geothermal anomaly. In an up-gradient group of springs and wells, incomplete TSR progress that is limited by energy from electron donors is evident from: low concentrations of dissolved sulfide with low Î´34S values (as low as âˆ’ 21.9â€°), a large balance of remaining as SO42âˆ’
- Original Version:
- Chemical Geology, Vol. 271, no. 1-2 (2010-03-01).
- Source Institution:
- University of South Florida Library
- Holding Location:
- University of South Florida
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- This object is protected by copyright, and is made available here for research and educational purposes. Permission to reuse, publish, or reproduce the object beyond the bounds of Fair Use or other exemptions to copyright law must be obtained from the copyright holder.
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