MAGNETOSTRATIGRAPHY 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 the carbonates of the Ordovician Knox Group, and is hypothesized to have originated as a paleo-sink hole. 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. Plant material recovered includes leaves, seeds, nuts, wood, and pollen. Pine, oak, ash and hickory have been identified. The recovered biota suggests that the GFS preserves a closed forest environment. The presence of Teleoceros and Plionarctos currently constrains the age of the site to 4.5-7.0 Ma.

In order to better constrain the GFS age and depositional history, a composite section comprising of a 38.0 m core to Knox basement and a 12.0 m exposed section have been sampled for paleomagnetic analysis. All studies were carried out at the University of Florida Rock and Paleomagnetism Laboratory. NRM and bulk magnetic susceptibility data exhibit strong correlations to each other and to changes in core lithology. IRM studies and demagnetization behavior indicate that magnetite is the dominant carrier of the NRM. All samples were demagnetized using stepwise thermal (N=11) or alternating field (N=42) demagnetization. Nine thermal demagnetization samples were rejected from the study because of inconsistent results attributable to the high organic content of these sediments. AF demagnetization was very successful. The combined results from the composite section yield a magnetostratigraphy characterized by seven polarity reversals. Although no unique tie to the magnetic polarity timescale is possible with the current age constraints provided by vertebrate taxa, magnetostratigraphic data suggest that the GFS had a depositional history that exceeds 1.0 myr.