STRATIGRAPHIC AND GEOCHEMICAL SIGNATURES OF EOGENETIC PALEOKARST IN VISEAN CARBONATES, SOUTHEAST KENTUCKY

The thickness of Viséan Carbonates exposed along the western margin of the Cumberland Plateau, specifically the St. Louis and Ste. Genevieve limestone members of the Slade Formation, were partly influenced by the Rome Trough, an Ediacaran through Cambrian failed rift associated with the formation of the Iapetus Ocean. The margins of upthrown blocks of asymmetric half-grabens experienced significant stratigraphic thinning as well as erosion, brecciation, and paleosol development at sequence boundaries. Most significantly, unconformities truncated much of the St. Louis and Ste. Genevieve Limestone at these locations. Paleokarst features associated with these unconformities include lenses of siltstone dolomitized by diagenetic fluids that may represent eogenetic caves formed as stratiform voids at paleo-water tables.

We collected detailed morphology and stratigraphy data (photo mosaics and field sketches), mineralogy (Rigaku MiniFlex XRD), stable isotopes of carbon and oxygen (Thermo Scientific Gasbench II coupled to a Thermo Scientific Delta V Advantage IRMS), element geochemistry (Olympus DELTA Perkin Elmer Optima 2000DV ICP-OES), and trace metal analysis (Olympus DELTA Handheld pXRF—soil and mining modes) for three of these lenses of dolomitic siltstone. Samples comprised 2.5 cm-diameter rock plugs collected by hammer drill every decimeter along paired profiles through and adjacent to the feature. Silica-enriched dolomite distinguishes the features from the largely calcite host rock with lenses of chert within and overlying the features. Heavier isotopes (¹³C and ¹⁸O) are consistently enriched in the profile through the feature compared to the control profile. Element and trace metal chemistry has a more complex pattern of enrichment and depletion in the feature compared to the control profile. Collectively, these data present a detailed picture of the origin of the features and the geochemical overprinting from diagenetic fluids.