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

Abstract

collection of conodonts from middle to upper Silurian (uppermost Llandovery–Pridoli series) strata in the Appa­ lachian Basin was produced by Charles T. Helfrich during the 1970’s. Most of the work was completed as part of his Ph.D. dissertation (Helfrich 1972) and published in a series of papers (Helfrich 1975, 1978, 1980) that laid the foundation for Silurian conodont biostratigraphy in the Appalachian Basin. In total, more than 15,000 spe­ cimens were recovered from six sections in the West Virgi nia, Virginia, and Maryland tri­state area, with which he established the conodont biozonation for the Silurian succession of the east­central Appalachian Mountains. Helfrich’s work was carried out at the dawn of a major transition in conodont systematics, from form taxonomy to multi­element taxonomy, and relied on the original Silurian conodont biozonation of Walliser (1964) to establish a biostratigraphic zonation for the Appalachian Basin consisting of eight zones for uppermost Llandovery through Pridoli strata. Most reported specimens were identified as form species, typically with tentative multi­ element species designations in open nomenclature. Silur­ ian conodont taxonomy and biostratigraphy have advanced tremendously in the intervening decades (e.g., Barrick & Klapper 1976; Bischoff 1986; Aldridge & Schönlaub 1989; Kleffner 1989, 1995; Nowlan 1995; Jeppsson 1997; Männik 1998, 2007; Corradini & Serpagli 1999; Jeppsson & Aldridge 2000; Calner & Jeppsson 2003; Murphy et al. 2004; Jeppsson et al. 2006; Carls et al. 2007; Slavík 2014; Corradini et al. 2015; Männik et al. 2015; Mathieson et al. 2016; Waid & Cramer 2017a, b), however, no modern systematic revision to the conodont biozonation of the uppermost Llandovery to Pridoli interval of the east­ central Appalachian Basin has been undertaken. Herein, we provide a modern and revised conodont biozonation for the central axis portion of the Appalachian Basin based upon the conodont collection of C.T. Helfrich (Helfrich 1972, 1975, 1980) that was re­examined by the authors at the University of Iowa from 2015–2018. The Helfrich collection is housed at the Museum of Geosciences at Virginia Tech (Virginia Polytechnic Institute and State University).