CONODNT BIOSTRATIGRAPHY NEAR THE MISSISSIPPIAN/PENNSYLVANIAN SYSTEM BOUNDARY IN WESTERN KENTUCKY

Primarily to check their ages, conodonts were collected from the Pennsylvanian-age undifferentiated Caseyville Formation/Tradewater Formation and from a unit that has been mapped traditionally as the Leitchfield Formation of Chesterian (Mississippian) age in western Kentucky. The Caseyville/Tradewater exposure studied near Morgantown consists of gray and black shale and wackestone. The so-called Leitchfield Formation consists of gray shale interbedded with fine-grained sandstone rhythmites at the Butler-Warren County line (Durham Chapel site) and of interbedded rhythmites and black and gray shales and minor coal beds at the Manhattan Branch site.

Conodonts are uncommon at the Manhattan Branch site and the Durham Chapel site produced only one indeterminate element. The former, however, included three juvenile Idiognathodus Pa elements indicating a Pennsylvanian age, which is not in agreement with 1960's mapping. Previous work at both sites by the Kentucky Geological Survey, however, has suggested that these rocks are basal Pennsylvanian. On the bases of limited evidence, a Morrowan or Atokan age seems most likely.

The undifferentiated Caseyville/Tradewater section produced 188 identifiable elements dominated by Idiognathodus. Most important stratigraphically are Idiognathoides (Morrowan/Atokan) and morphologies of Neognathodus that suggest a late Atokan age. Hindeodus and Idioprioniodus are rare; Diplognathodus is represented by a single specimen and Ubanites by one questionable element. Conodont biofacies associations of the Caseyville/Tradewater reflect a shallow shelf, marine environment of generally low to moderately elevated energy.