SEDIMENT STARVATION IN THE CENTRAL AND DISTAL APPALACHIAN FORELAND BASIN DURING THE NEOACADIAN OROGENY, THE FLOYDS KNOB BED OF KENTUCKY, INDIANA, TENNESSEE AND VIRGINIA: CAUSES AND IMPLICATIONS

The Neoacadian orogeny is a Mississippian tectonic event that records the diachronous convergence of the Carolina terrane with the eastern margin of Laurussia. During the Neoacadian event, the major sedimentary manifestation in the Appalachian foreland basin included two westwardly prograding clastic wedges, the Borden-Grainger-Price-Pocono and Pennington-Mauch Chunk, separated by the prominent, shallow-water, Newman-Greenbrier-Slade-Monteagle carbonate interval. An important precursor event to the widespread deposition of the shallow-water carbonates was a brief late Osagean interval of delta diversion and sediment starvation that is represented by the Floyds Knob Glauconite Bed in central and distal parts of the Appalachian basin. The Floyds Knob Bed is represented by a thin horizon of pelletal glauconites, glauconitic carbonates, or glauconitic shales, less than a meter to a few tens of meters thick, across most of the Borden-Grainger delta platform, delta front, and prodelta and in the distal-most Fort Payne basin forward of the delta complex. Like most glauconites, they represent deposition in sediment-starved, mildly oxic to dysoxic, marine settings deeper than 60 m. The glauconites appear abruptly across various shallow- to deeper-water delta environments and record the near complete shut-off of clastic sedimentation on the Borden-Grainger delta complex. Review of Neoacadian flexural history in the area suggests that the delta diversion and sediment shut-off were accomplished by eastward bulge return during loading–type relaxation in high-stand conditions such that the bulge blocked and diverted westwardly prograding sediments; during the ensuing sediment-starved conditions, glauconite was deposited in various forms across former deltaic and basinal settings in the central and distal foreland basin. Moreover, the delta platforms and sediment shut-off set the stage for the widespread deposition of carbonates (Newman-Greenbrier-Slade-Monteagle formations) throughout the basin during succeeding lowstand and subtropical conditions. Clearly, tectonic and flexural causes, when integrated with eustatic and paleoclimatic conditions, may exert major control on the nature of foreland-basin infill.