CONODONT BIOSTRATIGRAPHY AND BIOFACIES OF LOWER MIDDLE DEVONIAN LIMESTONES, NORTH-CENTRAL OHIO

Strata of the Detroit River Group of north-central Ohio reflect restricted conditions of sedimentation during early Eifelian (early Middle Devonian) time that were transgressively displaced by normal-marine environments represented by the Columbus Limestone, which ranges from the middle costatus costatus Zone into the australis Zone and is capped by a disconformity interpreted as a wave-eroded surface. The overlying Delaware Limestone is assigned with uncer- tainty to the kockelianus Zone and reflects renewed transgression followed by a regressive phase. Biofacies interpretation attributes a planktonic or nektonic habit to species of Belodella, Coe- locerodontus, and Icriodus. Distribution of species of Polygnathus suggests they were benthic or nektobenthic creatures with sensitivity to energy level and substrate texture. Prioniodinacean elements are mainly restricted to facies reflecting sedimentation below normal wave base. New taxa introduced include Icriodus stephensoni n. sp. and Polygnathus linguiformis alingulatus n. subsp. Several other forms that are either new or of uncertain taxonomic position are left in open nomenclature.