Transgressive wave ravinement on an epicontinental shelf as recorded by an Upper Pennsylvanian soil-nodule conglomerate-sandstone unit, Kansas and Oklahoma, U.S.A.

Abstract

A thin (3–25 cm), persistent conglomerate-sandstone unit occurs at the base of the transgressive systems tract of an Upper Pennsylvanian cyclothem below a transgressive limestone in outcrop and subsurface in SE Kansas and NE Oklahoma. It has an erosional base and a sharp top, and is composed of calcitic clasts, some shell fragments and quartz sand, and rare coal fragments. Clasts are rounded, equant-to-elongate, coarse sand-to-pebble sized, and moderately to well sorted. They are micritic to microsparitic or radial fibrous calcite grains and pisoids. Micritic and microsparitic clasts are heterogeneous and contain rounded to elongate moulds and radiating or concentric, spar or micrite-filled cracks. Pisoids have micrite cores and superficial calcite or clay rims. The clasts have similar texture and composition to the calcitic nodules and rhizoconcretions in underlying paleosols, and thus were probably derived from these soil nodules. Upper shoreface erosion during shoreline transgression excavated the underlying paleosols and eroded coeval transgressive deposits landwards of the shoreline. The eroded sediments were then reworked and transported to the lower shoreface and inner shelf by storm return flows to be deposited as a soil-nodule conglomerate-sandstone unit. Its base is an amalgamated surface of wave ravinement and initial transgression as well as the lower sequence boundary. The widespread conglomerate-sandstone unit suggests extensive transgressive wave ravinement on an epicontinental shelf. The transgressive record composed of upward-deepening, dominantly fine-grained lithofacies defines a new type (T-C 4) of transgressive record, which is composed of mixed carbonate and siliciclastic lithofacies with a simple transgressive lag on a low-relief shelf.