Divergent Geochemical Pathways of Carbonate Aquifer Evolution in a Classic Karst Terrain: (1) Polygenetic Cave Development Identified Using Longitudinal Groundwater Geochemistry

• Published in: Water
• Main Authors: Sarah A. Burgess, Lee J. Florea, Tracy D. Branam
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2023
• Subjects: water chemistry; stable isotopes; Mitchell Plateau; lost river; Bluespring Caverns; Hydraulic engineering; TC1-978; Water supply for domestic and industrial purposes; TD201-500; Lost River; St. Louis; Carbonic acid
• Online Access: https://doi.org/10.3390/w15193410; https://doaj.org/article/4ce784cbcd4d4544ad2bd9516964b6f9

Carbonic acid and sulfuric acid speleogenesis describe a dichotomy between epigenetic and hypogenetic caves and carbon and sulfur cycling in karst, but do not acknowledge the global spectrum of cave formation. This paper, part one of a two-part investigation, tests and revises speleogenetic models from a classic karst landscape using dissolved ion concentrations δ 13 C DIC , and δ 34 S in water samples collected at four sites across the Bluespring and Lost River karst basins in the Mitchell Plateau, Indiana, USA. Analyses revealed elevated sulfur in both karst basins but differently sourced; H 2 S (δ 34 S = −14.2‰) evolved from petroleum seeps in Bluespring Caverns accounted for up to 61% of sulfur in the cave stream, while evaporite beds (δ 34 S = [+14.50‰, +17.91‰]) of the St. Louis Limestone contributed up to 100% of sulfur at Orangeville Rise, a terminal spring of the Lost River karst basin. These results have implications for carbon–sulfur cycle linkages, particularly the potential acceleration of carbon flux from sulfuric acid dissolution in otherwise epigenetic settings. We suggest a new paradigm for speleogenesis in the North American midcontinent—speleogenesis in the Mitchell Plateau and similar settings is not epigenetic or hypogenetic, but instead polygenetic with competing chemical processes varying across space and time.