CARBONIFEROUS-PERMIAN STRATIGRAPHY OF THE MIDCONTINENT

The Admire, Council Grove and lower Chase Groups of Kansas, Oklahoma and Nebraska are placed into three third-order depositional sequences, an Admire late highstand sequence set, a Council Grove transgressive and highstand sequence set, and a Chase transgressive sequence set. Sequences are defined by bounding maximum exposure surfaces and placed within the zone of exposure surfaces (typically, stacked paleosols). Conodonts are abundant in open marine deposits and most marine units have a distinctive faunal make-up. Several of the maximum flooding surfaces have the introduction of new conodont species, including the index species that define the base of the Asselian, Sakmarian, and Artinskian. Streptognathodus isolatus, index to the Asselian, occurs at the base of the Bennett Shale Member of the Red Eagle Limestone, Sweetognathus merrilli, index to the Sakmarian, occurs in the Eiss Limestone Member of the Bader Limestone and Sweetognathus whitei, index to the Artinskian, occurs in the Florence Limestone Member of the Barnston Limestone. Generally, cyclothemic-scale depositional sequences from the Admire, Council Grove, and Chase groups comprise a two-component (hemicycle) system, one being carbonate-dominated and the other siliciclastic-dominated, representing dominantly marine and terrestrial-marginal marine deposition, respectively. Species of the conodont genus Streptognathodus are placed into three phylogenetic lineages exemplified by S. barskovi, S. isolatus, and S. elongatus. The varying changeover in species within each lineage produces a different faunal make-up for almost every carbonate hemicycle, potentially allowing for correlation of each maximum flooding surface not only by its physical stratigraphy, but its conodont composition as well.