Telychian (Llandovery, Silurian) conodonts from the Chimneyhill Subgroup, West Carney Hunton Field, North-Central Oklahoma



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Twenty-eight cores from the West Carney Hunton Field (Logan and Lincoln Counties, Oklahoma) yielded late Llandovery (Silurian) conodont faunas from the Chimneyhill Subgroup of the Hunton Group. Five cores yielded late Llandovery (Telychian) conodonts from a previously unknown stratigraphic unit that lies between the Cochrane (Llandovery) and Clarita (Wenlock) formations. The main part of the field is a reef-dominated carbonate shoal consisting of reef facies in the Cochrane and lagoonal facies in both the Cochrane and the new Telychian unit. The lagoonal facies is a complex of pentamerid brachiopod mounds flanked by crinoid-, brachiopod- and/or coral-dominated grainstones. The Telychian lagoonal facies fauna includes Pterospathodus a. amorphognathoides, Pt. a. lennarti, Pt. a. angulatus, Pt. celloni, Ozarkodina polinclinata polinclinata, Ozarkodina polinclinata estonica, and Aspelundia fluegeli? Species of Pterospathodus and Ozarkodina allow recognition of the Telychian Pt. eopennatus through Pt. a. amorphognathoides zones of Männik, which are based on sections in the Baltic region. Two cores in nodular shaly limestones, dolostones, and shale yield deeper water faunas containing Aulacognathus bullatus, Aul. kuehni, Aul. latus, and Oulodus sigmoideus? Three successive biozones based on species of Aulacognathus (Aul. bullatus, Aul. kuehni, and Aul. latus in ascending stratigraphic order) are recognized. The lack of Pterospathodus in the deeper water fauna makes it difficult to correlate this fauna to the lagoonal facies and to the standard Silurian conodont zonation. The occurrence of Pt. a. amorphognathoides at the top of the deeper water cores and the presence of Oz. polinclinata in the lagoonal facies indicates that they are contemporaneous. Many of the species of these Telychian faunas have been found previously in southern Oklahoma only as elements reworked into Late Silurian strata, but the strata from which they originated were unknown.