Paleodepositional Setting of Rhodoliths from the Upper Pennsylvanian (Virgil) Salem School Limestone of Northcentral Texas

Abstract

During Late Pennsylvanian time (Upper Carboniferous-Stephanian), much of the midcontinent United States comprised a slowly subsiding open marine carbonate shelf in which limestone deposition was prominent, although shales and sandstones were also deposited. This region is further exemplified during this time interval by the excellent development of sedimentary cyclic deposition (Moore 1950). Recently, Toomey (1983a) presented the results of a detailed field and laboratory study of the “middle limestone member” of the Oread Limestone (Shawnee Group): the Leavenworth Limestone. This thin (less than 3 feet thick) limestone has long been regarded as a classic example of lateral homogeneity along outcrop for a distance of more than 300 miles. The persistent homogeneity is in part the result of deposition occurring essentially parallel to a Late Carboniferous epicontinental sea. Leavenworth microfacies distribution reflect this overall rock homogeneity in that most of the outcrop belt can be designated as a mud-supported skeletal wackestone. It is only at those localities, present in northern Oklahoma, where the Leavenworth enters and merges into sediments laid down within a clastic trough, that a facies change occurs. Here, the Leavenworth, as identified by detailed tracing of beds, by rock character, faunal associations, and stratigraphic position, changes microfacies to an oncolithic wackestone. This particular microfacies is characterized by the abundance of relatively large algally coated-grains composed of laminar thalli of the red alga Archaeolithophyllum lamellosum Wray. In northern Oklahoma, the Leavenworth Limestone, and all other thin Upper Carboniferous limestones, lens-out and merge into a clastic wedge of sediments derived from a paleo-highland source to the south (see Fig. 1). This source area, herein termed the Oklahoma Mountains, had initially been recognized by Powers (1928).