A COMPARISON OF IDIOGNATHODUS FAUNAS FROM THE UPPER SALESVILLE SHALE OF NORTH-CENTRAL TEXAS AND THE HUSHPUCKNEY SHALE OF OKLAHOMA, KANSAS, AND NEBRASKA

Detailed collections of the Upper Salesville Shale from North-Central Texas and the Hushpuckney Shale of Kansas and adjacent states (Midcontinent Basin) have yielded correlative conodont faunas. A taxonomic system using characters of functional significance and biometrics was used to compare the Idiognathodus species of the two faunas. The Midcontinent fauna has a higher species diversity than the Texas fauna, but key species for correlation have been identified in both regions. Idiognathodus swadei and I. cancellosus are present in both the Midcontinent and Texas faunas. Idiognathodus cancellosus is restricted to the Hushpuckney Shale (Swope Cyclothem) and the overlying Stark Shale (Dennis Cyclothem) in the Midcontinent Basin. Idiognathodus swadei is not present in the Stark Shale, while it is found in the Hushpuckney Shale. The presence of both I. swadei and I. cancellosus in the Upper Salesville Shale confirms the correlation to the Hushpuckney Shale (Swope Cyclothem) of the Midcontinent.

Study of idiognathodid conodonts in the Midcontinent Hushpuckney Shale indicates three populations within the basin. A basinal population (Oklahoma), a high shelf population (Nebraska) and a lower-mid shelf mixed population (Kansas) have been identified using the dominance of Idiognathodus species characteristic within each population. The basinal population is dominated by specimens with reduced or missing accessory lobes including I. cancellosus, I. corrugatus, and I. folium. Other species present include I. sulciferus, I. swadei, I. lobatus, I. biliratus, I. clavatulus, I. turbatus and I. siculus. The high shelf population is dominated mostly by species with robust accessory lobes including I. sulciferus, I. cancellosus (reduced lobes), and I. swadei. The high shelf population contains the other species found in the basinal population, with the notable absence of I. biliratus. The lower-mid shelf mixed population is dominated by I. corrugatus, I. cancellosus, I. swadei, and I. sulciferus and shares the same species as the basinal population, including I. biliratus. The Upper Salesville Shale fauna is most similar to the high shelf population in that it is dominated by I. sulciferus, I. swadei, and I. cancellosus. The lack of I. biliratus in the Upper Salesville Shale further supports this relationship.