STRATIGRAPHY AND PALYNOLOGY OF THE MIO-PLIOCENE GRAY FOSSIL SITE, WASHINGTON COUNTY, EAST TENNESSEE

The Gray Fossil Site (GFS) is a Mio-Pliocene locality in eastern Tennessee that has preserved a diverse suite of vertebrate, invertebrate and plant remains. The deposit occurs within carbonates of the Ordovician Knox Group, and is hypothesized to have originated as a paleo-sink hole. Sediment samples have been collected from approximately 12.0 m of exposed section within the feature and from a 37.0 m core (GFS-1) drilled to basement. The sediments are generally dark and are dominated by cyclic couplets of organic rich clay and fine silt units, interpreted to have been deposited in a standing body of water. The fine sediments are occasionally interrupted by sands and/or gravel stringers, and boulders, some having diameters in excess of 3 m, which occur at various horizons across the site. The organic rich sediments, indicative of anoxic water conditions, may well be the reason for the large volume and remarkable preservation of the GFS biota. The vertebrate fauna is dominated by tapirs, but includes fish, frogs, alligators, turtles, snakes, lizards, rhinoceros, camels, deer, a bear, a saber-tooth cat, a shrew, a gompthothere, a hyaenid and a panda. The site is notable for the absence of horses. The presence of Teleoceras and Plionarctos currently constrains the age of the site to 4.5-7.0 Ma. Recent paleomagnetic studies of GFS-1 indicate that most of the core is of reverse polarity. The combination of vertebrate fossil and paleomagnetic data constrain the duration of deposition to < 700 ka. Plant material has been preserved in remarkable condition and volume and includes leaves, seeds, nuts, wood, and pollen. Identified plant macro fossils include pine, multiple species of oak, ash and hickory. A total of 36 samples were collected from GFS-1 for pollen analysis. The pollen population is dominated by Pinus (pine) and Quercus (oak) but includes a variety of other deciduous taxa, Salix (willow), Cyperaceae (sedges), and minor grasses. Both the pollen and the plant macros indicate that the GFS sink hole was dominated by closed forest taxa and that grasses were a minor component. These findings support previous interpretations of the site, based on recovered vertebrate taxa and the notable absence of horses, as a closed forest environment and possibly a refugia.