EVOLUTION OF MATRIX POROSITY AND ITS EFFECT ON CAVE PASSAGE DEVELOPMENT

Previous work on cave morphology has focused on relationships between cave passages and hydrologic or general geologic controls, without in-depth petrological work. As a pilot project, we studied cave-passage morphology and petrographic characteristics of Mississippian carbonates (Slade Formation) in Spelungers Cave, Wayne County, Kentucky. Survey data and field observations record passages oriented along faults, suggesting strong structural control on speleogenesis. Here, elongate, irregularly shaped dolomite bodies occur that cross-cut bedding surfaces of the surrounding limestone and protrude into cave passages to varying degrees. The current data support a paleokarst origin of these features, namely, eogenetic caves developed during relative sea-level lowstands during the deposition of the Ste. Genevieve Limestone. Subsequent sea-level rise renewed carbonate sedimentation and filled the cavities with lime mud. Later dolomitization was restricted to the paleokarst fill, likely because of porosity and permeability contrasts between the cave-filling sediment and the surrounding limestone (bioclastic wackestone and bioclastic/ooid grainstone), resulting in highly porous dolomite bodies encased in tight limestone. The presence of crinoid fragments and minor detrital quartz grains in the otherwise fabric-destructive planar-e matrix dolomite support this scenario. Later, likely in a more deeply buried setting, the intercrystal pore spaces in the dolomite bodies were filled with nonferroan and ferroan calcite. This late calcite cementation rendered the dolomite tightly cemented and, coupled with the lower solubility of dolomite compared to calcite, more resistant to cave-passage formation than the surrounding limestone. The differences in protrusion between two studied dolomite bodies are likely caused by differences in weathering resistance between the softer wackestone (more receded) and the harder grainstone (less receded) surrounding the dolomite bodies. Upcoming geochemical analysis, dissolution experiments, and numerical modeling will help us better understand how dolomitization and other diagenetic events affected the development and distribution of matrix porosity and may have controlled the development and distribution of flow paths of the dissolving fluids.