Preliminary Reassessment of Upper Ordovician (Sandbian-Katian) Conodont Biostratigraphy at Dolly Ridge, West Virginia and Its Integration with Tephrochronology and Graptolite Biostratigraphy
The temporal framework of the Nealmont Formation to Dolly Ridge Formation succession exposed at Dolly Ridge, West Virginia is of interest because it contains multiple K-bentonites and evidence of the Guttenburg carbon isotope excursion (GICE). Previously published work suggested that the top of the Dolly Ridge Formation is the base of the Belodina confluens Zone. The GICE is reported at other locations to begin in the lower part of the P. tenuis Zone and end at the start of the B. confluens Zone. We collected 14 samples throughout the upper Nealmont and Dolly Ridge formations for conodonts in an effort to improve the conodont biostratigraphic resolution and to place the GICE and K-bentonite beds into a more complete biostratigraphic framework. Three samples were collected in the upper Nealmont. They contain a fauna of Curtognathus sp., Drepanoistodus suberectus, Erismodus sp., and Plectodina sp. This sparse fauna consists of long-ranging taxa that does not better constrain the age of the top of the Nealmont. The Dolly Ridge Formation is approximately 91 meters thick. Samples were taken approximately 10 meters apart throughout the formation. With one exception, conodont recovery was low. The lower part of the Dolly Ridge Formation has a conodont fauna that includes Amorphognathus tvaernensis, Dapsilodus? sp., Drepanoistodus suberectus, Panderodus gracilis, Phragmodus undatus, and Yaoxianognathus abruptus. The upper part of the Dolly Ridge Formation has a conodont fauna consisting of Belodina sp., Curtognathus sp., Drepanoistodus suberectus, Erismodus sp., Panderodus gracilis and Phragmodus undatus. Three Belodina elements recovered are fragmentary and key elements in identifying the species of Plectodina are absent. The fauna recovered so far does not help to better resolve a biostratigraphic framework for the K-bentonites or for the GICE. Further collecting to enable a higher resolution conodont biostratigraphy integrated with tephrochronology and graptolite biostratigraphy is underway.