TOWARD A MORE COMPREHENSIVE MODEL OF KARST DEVELOPMENT IN THE U.S. MIDCONTINENT

A growing suite of data from karst landscapes in the U.S. midcontinent, including cave morphology, host rock petrology, secondary mineralization, and groundwater chemistry, suggests multigenerational cave development inclusive of epigenetic and hypogenetic processes. In this presentation we summarize examples from the Cumberland and Mitchell plateaus of Kentucky and Indiana, respectively, and expand toward a larger picture of how geologic structure, fluid chemistry, and changing climate lead to cave systems that retain signatures of a complex past.

Groundwater investigations in the Cumberland Plateau led to geochemical models that ascribe a significant portion of measured DIC flux to the influence of sulfur redox. The sulfur clearly associates with entrained brines rising through geologic structures and into karst aquifers. The resultant caves are largely in an epigenetic flow field of meteoric waters, with present development guided by staged base-level incision, but they retain indicators of speleo-inception by hypogenetic fluids.

Similarly-organized groundwater investigations in the Mitchell Plateau have revealed different influences of sulfur on DIC flux and speleogenesis in adjacent karst aquifers. Where hydrocarbon-sourced sulfides rise through fracture systems, cave development and DIC flux may be enhanced by sulfuric acid speleogenesis, especially during early fracture enlargement. In contrast, when nearby karst waters at calcite equilibrium encounter and dissolve sedimentary evaporite, the common-ion effect drives the precipitation of calcite and can sequester DIC.

Alongside these ongoing geochemical processes are stratigraphic, morphologic, and chemical fingerprints of karst development that occurred more than once in the history of the host rock of both settings. These paleokarst features comprise the association of lenticular dolomite bodies with eogenetic caves and emplacement of MVT minerals and calcite spar during late Appalachian distal tectonics.