ABSTRACT During latest Devonian to Middle Mississippian parts of the Neoacadian and Ouachita orogenies, the Appalachian Basin and parts of the Illinois Basin were filled with clastic debris derived from the westward-prograding Borden-Grainger-Price-Pocono clastic wedge. This delta complex is overlain by the widespread shallow-water Newman–Greenbrier–Slade–St. Louis–Warsaw–Salem–Harrodsburg carbonate interval across sediment-starved surfaces, comprising the Floyds Knob bed or interval. The Middle Mississippian (late Osagean; early Viséan) Floyds Knob interval is less than a meter to several meters thick and is composed of multiple zones of pelletal glauconite, finely divided glauconitic shales, glauconitic carbonates, and locally derived carbonate mud mounds. The interval occurs across most of the Borden-Grainger delta platform, delta front, prodelta, and within the starved-basin area seaward of the delta complex, which was then filled with the Fort Payne Formation. This study reports herein the first occurrence of the Floyds Knob interval within the Fort Payne Formation. Glauconite deposition in this interval apparently occurred in mildly oxic to dysoxic, sediment-starved, shallow-marine settings and is believed to represent termination of major clastic influx in more proximal parts of the Neoacadian foreland basin during lowstand conditions. Moreover, these starved-basin conditions can be correlated with delta diversion following bulge migration during flexural loading–type relaxation. During these sediment-starved, lowstand conditions, glauconite was deposited across deltaic and basinal settings in central and distal parts of the Neoacadian foreland basin, as well as in eastern parts of the present-day Illinois intracratonic basin. The cessation of deltaic clastic sedimentation permitted development of carbonate mud mounds and associated glauconitic shales on and near reactivated structures in central parts of the Fort Payne starved basin and set the stage for the widespread deposition of thick, Meramecian–Chesterian carbonates throughout the basins during succeeding subtropical and lowstand conditions. Whether less-than-a-meter or tens-of-meters thick, the Floyds Knob interval is a widespread Middle Mississippian chronostratigraphic interval in the east-central United States that reflects a change in tectonic regime, which is recorded in the shift from predominantly clastic to carbonate sedimentation across a broad region. Aside from its correlative value, the unit demonstrates consequent sedimentary responses to the interplay among tectonism, paleoclimate, and paleogeography.

Abstract In latest Devonian time, the collision between Avalonia, the New York promontory and Carolina terrane under the impact of Gondwana, generated an orogeny that began in New England and migrated southward in time. Once thought to be the fourth tectophase of the Acadian orogeny, this event is now called the Neoacadian orogeny. Active deformational loading during the event initially produced the Sunbury black-shale basin, whereas subsequent relaxational phases produced the Borden-Grainger-Price-Pocono and Pennington–Mauch Chunk clastic wedges, which largely reflect the dextral transpressional docking of the Carolina terrane against the Virginia promontory and points southward. The Sunbury black-shale basin and the infilling clastic wedges are among the thickest and most extensive in the Appalachian foreland basin. This trip will demonstrate differences in basinal black-shale and deltaic infilling of the foreland basin, both in more active, proximal and in more distal, sediment-starved parts of the basin. In particular, we will examine relationships between sedimentation and tectonism in the Early-Middle Mississippian Sunbury/Borden/Grainger/Fort Payne delta/basin system in the western Appalachian Basin during the Neoacadian Orogeny. We will emphasize the interrelated aspects of delta sedimentation, basin starvation, and mud-mound genesis on and near the ancient Borden-Grainger delta front. Temporal constraints are provided by the underlying Devonian-Mississippian black shales and by the widespread Floyds Knob Bed/zone, a dated glauconite/phosphorite interval that occurs across the distal delta/basin complex.

Abstract High-resolution sequence stratigraphic cross sections (based on outcrops and shallow cores) of Mississippian (Meramecian to Chesterian) strata in the Appalachian Basin, Kentucky, U.S.A, are the marine stratigraphic record of the interaction of tectonics on a slowly subsiding distal foreland, with the Carboniferous glacio-eustatic transition into icehouse conditions. Late Mississippian paleoslopes were to the southeast into the foreland basin, probably because of thrust loading and accompanying block faulting of the distal foreland. The succession is dominated by fourth-order sequences that are only a few meters to 15 meters thick, which is an order of magnitude thinner than those of the proximal foreland. Regional disconformities marked by paleosols, caliche, micro-karsting, brecciation, tepee formation, or sharp contacts between limestone and the overlying transgressive marine shale bound fourth-order sequences. The sequences are stacked into several siliciclastic-bounded third-order or composite sequences that make up the broadly transgressive Mississippian supersequence. Facies are dominated by oolitic grainstones passing downslope into skeletal grainstone-packstone and updip into lagoonal muddy carbonates, green shale, eolianites, and rare red beds. Marine shales occur at bases of the younger sequences. The fourth-order sequences can be correlated from the Appalachian distal foreland, into the proximal foreland, as well as into the intracratonic Illinois Basin, suggesting a eustatic origin. However, local and regional tectonics strongly influenced thickness and distribution of sequences as well as the distribution and timing of unconformities locally. The facies stacking in the lower sequences indicates that they formed under the influence of moderate sea-level changes that effectively flooded the ramp to depths of 10 m or less. This resulted in grainstones within sequences being partitioned by caliches and muddy carbonates near or at sequence boundaries. Facies stacking in the upper sequences suggests that the magnitude of fourth-order sea-level changes increased in the later Chesterian, causing flooding of the ramp to depths of tens of meters, probably synchronous with buildup of ice sheets on Gondwana. This was accompanied by a change to more humid climates, which decreased oolite deposition on the ramp and favored deposition of open marine skeletal limestones bounded by marine siliciclastic units. Such moderate-amplitude global eustasy may account for the widespread, highly partitioned grainy reservoirs typical of the Mississippian worldwide.