(1) Wichita State University, Wichita, KS
ABSTRACT: Transgressive Ravinement on an Epeiric Shelf as Recorded by a Limestone Conglomerate in the Upper Pennsylvanian Leavenworth-Heebner-Plattsmouth-Heumader Depositional Sequence, SE Kansas and NE Oklahoma
The TST of the Leavenworth-Heebner-Plattsmouth-Heumader sequence overlies multi-story calcareous paleosols and consists of basal Gleysol and carbonaceous shale (10s cm), middle limestone conglomerate (5-25 cm), and upper fossiliferous shale and Leavenworth Limestone (1-2 m). The conglomerate was observed in 15 outcrop sections covering 100 km, and interpreted in 14 wireline logs 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-granule in size, and moderately sorted. They include micritic and radial-fibrous calcite grains, and pisoids. Micritic grains contain quartz silt, radiating and/or concentric spar-filled cracks, and rounded central molds filled with micrite or spars. Pisoids have micritic-clast cores and concentric micritic 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 calcareous paleosols and, thus, were probably derived from soil nodules.
The calcareous paleosol-Gleysol transition indicates a semi-arid to subhumid climatic change, and an elevated groundwater table associated with shoreline transgression. Gleysols developed in coastal-marginal-marine environment. The limestone conglomerate is the first transgressive marine deposit. Its persistent thickness and composition suggest significant regional excavation of underlying calcareous paleosols and landward transport and deposition of soil-nodule clasts. Transgressive seas caused peneplanation on the vast epeiric Kansas shelf where homogeneous transgressive Leavenworth Limestone was deposited. An extensive ravinement surface may be present basinward of the study area.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.