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...

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