Silurian conodont biostratigraphy of the east-central Appalachian Basin (eastern USA): Re-examination of the CT Helfrich Collection

The conodont biozonation for the Silurian succession in the Appalachian Basin was established by C.T. Helfrich nearly half a century ago. Herein, we re-examined and updated the taxonomy of the conodont fauna and the consequent biozonation of the upper Rose Hill, Mifflintown, Wills Creek, and lower Tonoloway formations in the east-central Appalachian Basin. While these strata span the upper Telychian Stage (Llandovery Series) to the upper Pridoli Series, a major stratigraphic gap representing most of the Ludlow Series (from the lower part of the Gorstian to the upper part of the Ludfordian stages) was identified. The new conodont biozonation consists of the Pterospathodus amorphognaihoides amorphognathoides Zonal Group, an Unzoned Interval of the Sheinwoodian Stage, the Kockelella walliseri Zonal Group, the Ozarkodina bicornuta Zone, an Unzoned Interval of the Homerian Stage, the Ozarkodina bohemica Interval Zone, the Ozarkodina crispa Zone, and the Ozarkodina eosteinhomensis sensu law Interval Zone. This refined biozonation permits enhanced global correlation of the Silurian within the east-central Appalachian Basin.