Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the Cerna Valley, Romania

Citation

Material Information

Title:
Sulfur isotopic composition and the source of dissolved sulfur species in thermo-mineral springs of the Cerna Valley, Romania
Series Title:
Chemical Geology
Creator:
Wynn, Jonathan G.
Sumrall, Jonathan B.
Onac, Bogdan P.
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Sulfur Isotope ( local )
Sulfate Reduction ( local )
Thermo-Mineral Springs ( local )
Sulfide ( local )
Sulfate ( local )
Genre:
serial ( sobekcm )

Notes

Abstract:
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 TSR—a fact that likely reflects rapid redox cycling at low grade hydrothermal temperatures. δ13C values of dissolved inorganic carbon (DIC) are consistent with TSR using methane as an electron donor. δ34S 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 + 16‰, consistently pointing to dissolved S that derives from marine-derived sulfate mineral sources. To this combined S–C isotope data set, we apply a model of Rayleigh distillation which describes exponentially increasing δ34S values of a diminishing sulfate reservoir during TSR, and linearly decreasing δ13C 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 δ34S values (as low as − 21.9‰), a large balance of remaining as SO42−
Original Version:
Chemical Geology, Vol. 271, no. 1-2 (2010-03-01).

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University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
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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