CONODONT BIOSTRATIGRAPHY OF PORTIONS OF THE FORT SCOTT AND PAWNEE FORMATIONS, MARMATON GROUP (DESMOINESIAN, PENNSYLVANIAN), EASTERN KANSAS

The purposes of this study are to describe the conodonts from parts of the Fort Scott and Pawnee Formations of the Marmaton Group in eastern Kansas and adjacent Missouri and to use the conodonts for evolutionary and biofacies studies and for correlation. The Fort Scott members studied are the Little Osage Shale, a gray and black shale and gray wackestone, overlain by the Higginsville Limestone, a gray wackestone to packstone. The Pawnee members are the basal black Anna Shale, the Myrick Station Limestone, a gray wackestone and packstone, the gray to black Mine Creek Shale, and the Laberdie Limestone, a gray lime mudstone.

Idiognathodus dominates faunas in both formations. Hindeodus, Idioprioniodus, and Neognathodus are locally common. Ubinates, Adetognathus, and Diplognathodus are rare; Gondolella is absent from all lithologies. Plots of the numerical distribution of morphotypes of Neognathodus in any one unit form a bell curve, and the dominant point on the curve shifts through time to a simpler form. By comparing morphotype averages for Neognathodus populations, the Fort Scott cycle is a little more than half of a zone older than the Pawnee cycle. In spite of the broad trend toward simplification within Neognathodus, in both formations more primitive forms succeed more advanced ones upward. We suggest that more advanced morphs were introduced into the population from favorable offshore environments at the inception of each sequence along initial flooding surfaces. Subsequently, the influence of localized environmental conditions unfavorable to the advanced forms within the plexus favored higher survival rates among the more primitive morphs.

Conodont biofacies associations of both formations reflect a shallow shelf, marine environment of low to moderately elevated energy. Elevated numbers of Hindeodus reflect localized higher energy conditions while elevated numbers of Idioprioniodus in the black shales indicate deposition in very low energy, low oxygenated marine water. Locally elevated numbers of Adetognathus represent euryhaline conditions.