TRANSGRESSIVE SHOREFACE EROSION AND WAVE RAVINEMENT ON AN EPEIRIC SHELF AS RECORDED BY A SOIL NODULE CONGLOMERATE-ARENITE IN THE UPPER PENNSYLVANIAN OREAD CYCLOTHEM, SE KANSAS AND NE OKLAHOMA

The transgressive deposits of the Leavenworth-Heebner-Plattsmouth-Heumader minor cyclothem of the Oread Cyclothem overlie multi-story Calcisols and calcareous Vertisols and consist of basal Gleysol (10s cm), middle limestone conglomerate-arenite (5-25 cm), and upper fossiliferous shale and Leavenworth Limestone (1-2 m). The conglomerate-arenite was observed in 15 outcrop sections covering 100 km, and interpreted in 76 wells and cores in SE Kansas and NE Oklahoma. It is a single bed with conformable lower and upper contacts, composed of blackened clasts (80-95%), bedding-plane-parallel brachiopods, crinoids, and encrusting forams (5-20%), and rare coal fragments. Clasts are rounded, equant to elongate, coarse-sand-to-pebble size, and moderately sorted. They include micritic and radial-fibrous calcite grains, and pisoids. Micritic grains contain quartz silt, radiating and concentric spar-filled cracks, and rounded central molds filled with micrite or spars. Pisoids have micritic-clast cores and superficial micritic or ferruginous clay cortexes. Petrographically, the clasts have the same texture and composition as pebble-sized calcitic nodules, rhizoliths, and clasts of a channel-fill conglomerate in underlying paleosols and, thus, were probably derived from soil nodules.

Landward and upward shoreface translation during early transgression on a fluvial peneplain eroded the underlying calcareous paleosols and coeval early-transgressive deposits landward of the shoreline. The excavated soil nodules were reworked and transported to the inner shelf by storm return flows and were concentrated and deposited as a transgressive lag, i.e. the soil nodule conglomerate-arenite. The basal contact of the conglomerate-arenite is a wave ravinement surface, under which Gleysols formed by leaching and reworking of underlying paleosols by marine water. The persistent thickness and wide distribution of the conglomerate-arenite suggest extensive transgressive ravinement of the fluvial peneplain on the vast epeiric Kansas Shelf. The transgressive record is a typical T-C1 succession with a simple transgressive lag, composed of mixed carbonate and siliciclastic rocks.