A SANDSTONE MAPPED AS A BED IN THE ORDOVICIAN BAYS FORMATION IN BLOUNT COUNTY, TN IS REASSIGNED TO THE SILURIAN CLINCH SANDSTONE USING CONODONT BIOSTRATIGRAPHY

In 1965, along the western edge of the Great Smoky Mountains southwest of Knoxville, near Pumpkin Center, at the confluence of Harrison Branch and the Little Tennessee River, Robert Neuman and Willis Nelson mapped a “quartzite” in the upper Bays Formation (Ordovician). This quartz arenite is being studied to better understand its stratigraphic relationship to other Ordovician quartz arenites of similar age in this area. One possibility is that this sandstone is a thick exposure of the Walker Mountain Sandstone Member, or the “middle” sandstone member, both of which are units in the Bays Formation of Tennessee and Virginia. The purpose of our research is to assess the relative age of the sandstone in order to determine if belongs to the Bays Formation. Fieldwork in December 2016 revealed that an unmapped and ~40m thick limestone sequence underlies the quartz arenite and overlies typical redbeds of the Bays Formation; these limestones were evidently missed by Neuman and Nelson during their mapping in the 1950s and 1960s. We measured the section and collected twenty, 3 kg samples from beds in the limestone unit, and processed them for conodonts. The samples were not highly productive, but they did produce a meager fauna that contains Drepanoistodus suberectus, Plectodina tenuis, Panderodus gracilis, and Phragmodus undatus. This fauna indicates that the heretofore unmapped limestone unit between the quartz arenite above and the Bays Formation redbeds below is P. tenuis Zone or younger. Throughout the area of their occurrence in the Appalachians, the Walker Mountain Sandstone and “middle” sandstone members of the Bays are both stratigraphically downsection from the Deicke K-bentonite bed, and throughout its exposure the Deicke K-bentonite bed is below the P. tenuis Zone. We conclude, therefore, that both the unmapped limestones, and the sandstone mapped as being in the Bays Formation by Neuman and Nelson in the study area, are younger than the Walker Mountain Sandstone and “middle” sandstone members. Based on this new information, we suggest that the unmapped limestones are equivalent to the Upper Ordovician Trenton Group, and that the sandstone in the study area is most likely equivalent to, and an eastern outlier of, the Silurian Clinch Sandstone.