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 The Salem Limestone (Valmeyeran, Mississippian) is a preeminent dimensional limestone quarried in a two-county area of south-central Indiana for nearly 200 years. Advances in quarry technology in the past 30 years produce nearly smooth-sawn quarry walls that show the exquisite depositional details of the Salem carbonate shoal. The Salem shoal is part of a large-scale shoaling sequence that produced a carbonate platform during the middle Mississippian that began at the end of Borden Group (Mississippian) delta deposition and culminated with the deposition of the Ste. Genevieve Limestone (Mississippian). The Salem was deposited as a high-energy, but subtidal shoal above fair-weather wave base. Four environments are recognizable within the shoal: active shoal, open lagoon, intrashoal channel, and intershoal channel. A shoal crest environment may also be present as a fifth environment. A hierarchy of bounding surfaces can be defined using the sawed quarry exposures. First-order surfaces are foreset laminae and appear as inclined or horizontal stratification. Second-order surfaces are the contacts between similar bedforms, and third-order surfaces truncate first- and second-order surfaces, representing breaks in sedimentation. Combined they define mesoforms within the shoal complex. Fourth-order surfaces, similar to third-order surfaces, represent a change from a shoal to lagoonal setting. Evidence of hard-ground development occurs along third-order surfaces, associated with encrusting bryozoan holdfasts, corals, and columnar subtidal stromatolites. Tracing surfaces on the quarry walls is vital to reconstructing the internal architecture of the shoal and the processes that operated within it. We will examine this shoal architecture by visiting quarries and an outcrop, and we will visit a mill where quarried stone blocks are fabricated into panels and shapes for buildings.

Subaerial exposure surfaces in the Middle and Upper Mississippian Slade Formation of northeastern Kentucky are largely composed of cutanic concentrations of micritic calcite within the former Ccam horizons of caliche soils. The association of this material with soil horizons and structures, as well as with abundant root traces, strongly indicates a pedogenic origin. In fact, the contribution of plants and small soil organisms was far greater than has been previously recognized. The caliches occur as “interformational” profiles on disconformities separating lower Slade members and as “intraformational” profiles within three lower Slade units. Paleoexposure was related to position on a structurally active margin of the Appalachian Basin and to episodes of regional and local regression. The caliches resulted from soil and ground-water conditions in a semi-arid climate characterized by seasonal rain and drought and an overall net moisture deficit. Growth of roots, desiccation, and displacive crystallization broke up parent limestones, allowing access of vadose waters and creating framework (skeleton) grains that were easily transformed into a mobile plasma fraction by solution. Solution of carbonate grains and eluviation of carbonate-bearing solutions primarily occurred during the moist rainy season, whereas illuviation rapidly followed the onset of drought. The calcium carbonate was deposited largely as internal, laminar plasma concentrations called cutans, which have been incorrectly referred to as “crusts” in previous work on the Slade. Accumulation of these cutanic laminae formed indurated laminar calcrete deposits near the bases of the caliche profiles. These calcretes may be of physicochemical or rhizocretionary origin, depending on conditions of exposure. More diffuse, irregular calcretes apparently developed along avenues of porosity and were formed by plasma separation, the in situ micritization of other limestone textures. Although climate in the Meramecian and earliest Chesterian epochs was the major factor responsible for caliche formation, the length of exposure and the type of carbonate lithology controlled the nature and thickness of caliche profiles. “Intraformational” profiles are always thin and immature, representing short-lived exposure on porous lithologies like calcarenite. Conversely, “interformational” profiles are always mature or composite and represent longer periods of exposure on more impermeable lithologies such as calcilutite. Impermeable lithologies were important, because they prevented migration of soil waters and plasma below the soil profile. By late Early Chesterian time, the climate had become more humid, and the latest formed caliches were partially destroyed by solution, creating a leached, clayey residual soil on top of earlier caliche soils. On structurally elevated areas, where exposure was long and drainage was good, this period of humid pedogenesis resulted in composite terra rossa paleosols produced from the humid weathering of older caliche profiles.