THE BORDEN-GRAINGER-FT. PAYNE STRATIGRAPHIC COMPLEX OF THE APPALACHIAN BASIN, CENTRAL KENTUCKY, U.S.A.: THE SYNERGISTIC INFLUENCE OF TECTONICS, PALEOCLIMATE AND PALEOGEOGRAPHY

During the Middle Mississippian Neoacadian Orogeny, the Appalachian Basin filled with post-orogenic clastic debris from the westwardly prograding Borden-Grainger-Price-Pocono delta complex. The key to discerning relationships among all of these units is the sediment-starved Floyds Knob Bed, a Middle Mississippian (late Osagean) interval, centimeters-to-tens-of-meters thick, comprising multiple horizons of glauconite, glauconitic shales, glauconitic carbonates, and local carbonate mud mounds. The interval occurs across the Borden-Grainger delta platform, delta front, prodelta, and Fort Payne basinal area in front of the delta. Floyds Knob deposition records the end of major clastic influx due to the delta diversion in proximal parts of the Neoacadian foreland basin in lowstand conditions. During these conditions, glauconite was deposited across deltaic and basinal settings in central and distal parts of the Neoacadian foreland basin. The shut-off of deltaic clastic sedimentation permitted development of carbonate mud mounds and associated glauconitic shales on and near Ouachita-reactivated structures in central parts of the Ft. Payne Basin and set the stage for the widespread deposition of thick, Meramecian–Chesterian carbonates throughout the basin during succeeding subtropical, lowstand conditions. Moreover, a unique paleogeographic-paleoclimatic configuration at the time permitted upwelling of silica-rich waters from the Ouachita foredeep into the Ft. Payne basin, which may account for the silica-rich nature of the classic Ft. Payne. Whether thick or thin, the Floyds Knob is effectively a widespread Middle Mississippian chronostratigraphic interval that reflects a change in tectonic regime, which is recorded in the change from predominantly clastic to carbonate sedimentation across a broad region. Aside from its correlative value, the unit demonstrates the consequent sedimentary responses of the interplay between tectonism, paleoclimate and paleogeography.