BIOSTRATIGRAPHY OF THE OLENTANGY SHALE BETWEEN DELAWARE, OHIO AND MOREHEAD, KENTUCKY

The stratigraphic relationship between the greenish gray Upper Olentangy Shale at the type section in Delaware, Ohio and a younger green shale, the so-called “Olentangy” Shale, near Morehead, Kentucky has been interpreted based on conodont biostratigraphy. The latter was previously accepted as time-equivalent to the type Upper Olentangy Shale based on similarities in lithology, stratigraphic position beneath the Ohio Group Shales, and subsurface gamma ray logs. The type Upper Olentangy Shale occurs in the Frasnian MN Zone 13 with the uppermost beds occurring in the lowermost Famennian triangularis zone. The green “Olentangy” Shale in northeastern Kentucky is no older than the Famennian rhomboidea Zone. Thus, the type Upper Olentangy Shale and the “Olentangy” Shale are not time equivalent. The purpose of this study was to determine if these two green shales are time-transgressive or distinct. Based on conodont biostratigraphy in sections from three localities, Bainbridge and Peebles, Ohio and Herron Hill, Kentucky, the type Upper Olentangy Shale and the similar “Olentangy” Shale in northeastern Kentucky are independent. The section at Peebles, Ohio includes equivalents of both green shales, which are separated by approximately 2 m of black shale. Strata equivalent to the type Olentangy Shale may be absent in southern sections due to an unconformity that truncates progressively younger strata to the south.