Published online by Cambridge University Press: 20 May 2016
The borden formation in northeastern Kentucky contains a significant, largely undescribed, Osagean (upper Tournaisian to lower Viséan) ammonoid succession. Lower Osagean strata in the Nancy Member contain a diverse Pericyclus Zone assemblage characterized by Muensteroceras oweni (Hall), M. parallelum (Hall), Kazakhstania colubrella (Morton), Imitoceras ixion (Hall), and Masonoceras kentuckiense Work and Manger. This interval, which ranges into the basal Cowbell Member, was referred to the Muensteroceras oweni Assemblage Zone by Gordon and Mason (1985) and Gordon (1986) and indicates correlation to the lower Ivorian Stage of the Belgian Tournaisian succession. The succeeding middle Osagean interval in the middle and upper part of the Cowbell Member contains Merocanites drostei Collinson and Dzhaprakoceras which presumably represent the lower, or Tournaisian (upper Courceyan or lower Chadian), portion of the Fascipericyclus–Ammonellipsites Zone. An even higher middle Osagean assemblage with Polaricyclus bordenensis new species and Winchelloceras allei (Winchell, 1862) occurs in the upper part of the Nada Member, near the top of the Borden Formation, and is the basis for the current report.